The Manhattan Project is famously known as the United States‑led endeavor which successfully created the first atomic bomb. The success of the Manhattan Project led to the bombings of Nagasaki and Hiroshima in 1945 and the total surrender of Japan, ending World War II.

The project was extremely complex and dangerous, even causing the deaths of some of its own scientists. Nevertheless, its story is fascinating, and it is one of the most significant human achievements in history. Below are 10 fascinating facts about the Manhattan Project that shed light on the people, the science, and the legacy of this secretive wartime effort.

10 Einstein Was Integral To The Project Happening

The history of the Manhattan Project is often told as beginning with the Einstein‑Szilard letter. This famed missive, signed by Albert Einstein in 1939, was mailed to President Franklin D. Roosevelt. Leo Szilard, together with Eugene Wigner and Edward Teller, drafted the letter after realizing that a new, terrifying power was emerging from nuclear research—one that could unleash destruction unlike anything the world had ever seen and that Nazi Germany might harness.

Szilard arranged for Einstein to co‑sign the letter, which warned: “This new phenomenon would also lead to the construction of bombs,” and that such bombs “could be achieved in the immediate future.” The letter noted that Germany was already stockpiling uranium from Czechoslovakia, indicating a potential nuclear weapons program. Roosevelt received the warning and acted, creating the Advisory Committee on Uranium—effectively the first governmental step toward what would become the Manhattan Project in 1942.

9 The Project Was Infiltrated By Russia

The Manhattan Project was, for obvious reasons, top secret, and intelligence officials and the FBI did everything they could to keep Nazi Germany or Japan from learning about what was happening. Although the USSR were allies of the US, the US still wanted to keep them away from the project and avoid them benefiting from the research and testing being conducted. Despite this, the USSR managed to successfully infiltrate the Manhattan Project. Soviet intelligence had picked up on the fact that British and American publications into nuclear fission had recently dipped—a red flag.

Reportedly, Soviet spies were foiled at many attempts, but some managed to infiltrate the project and send back critical information—one of the most notable being Klaus Fuchs. Fuchs, a physicist, had secretly sworn allegiance to the USSR, offering his services to them. He had been assigned to the Los Alamos laboratory working on bomb research and design. He would pass on information to the USSR while working in Los Alamos and would be eventually caught after the war, confessing to everything. Other spies remain unknown to this day, and their identities were never uncovered by US counterintelligence.

8 The Project Cost Almost $2 Billion

The Manhattan Project was a complex effort, spread out over multiple sites across the US and Canada. The most important sites to the project were Oak Ridge in Tennessee and Los Alamos in New Mexico. Oak Ridge served as the main production plant, which produced the enriched uranium needed to create an atomic bomb. The Los Alamos site was a remotely located laboratory which was tasked with designing and building the bombs.

Many other sites fed into the project, and because of this, the costs added up. Much of the expense came from the Oak Ridge site. It was estimated that the total project costs were $1.9 billion, which would be well over $20 billion in today’s dollars.

7 The Project Was Deemed A Success

Despite the costs of the project being more than originally budgeted, despite the fatalities during the work, and despite all of the scientific challenges that occurred, the Manhattan Project was deemed a success. The overall objective of the project was to arm the US with an atomic bomb against the Nazi or Japanese threat of doing the same. However, whether the project really was a success is more of an ethical question than a factual one. The project delivered the only two atomic bombs ever detonated in warfare, with the total estimated deaths from those detonations being somewhere between 150,000 and 200,000 people.

The bombs ushered in a new nuclear era in which Russia and the US would emerge as superpowers, both armed with nuclear bombs, ready to destroy entire cities instantly. The bombings in Japan in 1945 brought about an abrupt end to the war and potentially saved many US lives, but the bombings today still pose a problematic question as to whether they were truly necessary and if they were morally correct. Some would argue they were a war crime; others would say they were justified and necessary. Without the “success” of the Manhattan Project, who knows who would have been the first country to use a nuclear bomb in World War II?

6 The Demon Core

According to reports, there were 24 fatalities during the Manhattan Project’s lifespan. Many of these were deaths caused by things like construction accidents. However, for scientists Harry Daghlian and Louis Slotin, it was a different case completely. Daghlian was a scientist who was working on experiments using the third nuclear core (with the first and second having been used in Japan). On August 21, 1945, Daghlian accidentally dropped a tungsten carbide brick onto the plutonium core assembly, which made the core go supercritical. He quickly got the brick off the core, but he would receive a lethal dose of radiation because of his accident and died in agony around a month later.

Despite this incident, nine months later, Slotin would die from the same core in another fatal accident. On May 21, 1946, Slotin was holding the top part of a beryllium neutron reflector in place above the core assembly with a screwdriver. (A recreation of the procedure is pictured above.) Then, his screwdriver slipped, and the half‑sphere fell totally onto the core. This slip caused a lethal amount of radiation to be released in a flash of blue light. Slotin quickly flipped the top part of the reflector off the core and onto the floor, neutralizing the threat. Nevertheless, he would die from acute radiation poisoning nine days later.

The plutonium core was later nicknamed the “Demon Core” because of its involvement in the two scientists’ deaths. It was later melted down, and its material was used in other cores.

5 Thin Man

In the early stages of the Manhattan Project, considerable research and attention was placed on designing a plutonium‑based “gun‑type” bomb. The work was code‑named “Thin Man,” in contrast to the “Fat Man” bomb dropped on Nagasaki. Fat Man worked by plutonium implosion, whereas Thin Man bombs would have worked by having two plutonium masses coming into contact with each other at high speed inside the bomb.

Thin Man was ultimately abandoned due to a number of difficulties experienced during research. Firstly, the bombs would have been 5.2 meters (17 ft) long, and this posed a challenge, as finding a suitable aircraft to carry them was difficult. Bombers could be modified to fit the longer casings, but it was later learned that the design of the two plutonium masses made the bombs likely to pre‑detonate. Because of this, the casings would have had to be extended, and this put the design outside the realms of what was possible to carry on an airplane of the time. This effectively spelled the end of the project. “Little Boy,” the bomb ultimately dropped on Hiroshima, was a gun‑type bomb, but it utilized uranium‑235 instead of plutonium‑239, as Thin Man bombs would have.

4 The Trinity Test Had Provisions In Case Of Disaster

One of the key milestones of the Manhattan Project was the Trinity test—the first‑ever detonation of a nuclear bomb. The test occurred on July 16, 1945, and was conducted by exploding “Gadget,” a device similar to Fat Man. The test was successful and quite literally started the atomic era.

Prior to the test, which was top secret, officials were forced to come up with ways to hide it from the public and press, which would prove difficult, considering the enormity of the predicted explosion. A writer for The New York Times, William Laurence, had been drafted into the Manhattan Project for this very reason. Laurence would help put together press releases that would cover up the events. Laurence wrote four press releases for the public attention the test would garner, with the most severe including a blank list of those people killed by the explosion and instructions for evacuation situations.

There was considerable worry that this press release would be needed. However, the press release ultimately used hid the event by attributing the noise and heat wave to a “remotely located ammunition magazine containing a considerable amount of high explosives and pyrotechnics” that had exploded.

3 The Project Was Not Based In Manhattan

Despite the name of the Manhattan Project, the bulk of the work conducted during its existence didn’t take place in Manhattan. In fact, as mentioned, the two most prominent sites were in New Mexico and Tennessee. During the project’s beginning, its official name was “Development of Substitute Materials,” but this never really stuck. President Roosevelt had assigned the project to the Army, and General Leslie R. Groves took up residence in Manhattan initially to draw on the nearby Corps of Engineers division.

Later, it was agreed that “Development of Substitute Materials” may have been too obvious, so they settled for “Manhattan District.” As the project expanded, and the need for multiple sites and laboratories became evident, the Army began to move away from Manhattan. However, the name followed them. Later on, the “District” part was used less and less until the project was known simply as the “Manhattan Project.”

2 The Doomsday Clock Was Born Out Of The Manhattan Project

After the closure of the Manhattan Project, many scientists were left ruminating about the overall impact the nuclear bomb would have in the future of the Earth. After the bombings of Nagasaki and Hiroshima, it’s not hard to see why. Therefore, in 1945, the Bulletin of the Atomic Scientists was created, and it began to publish monthly informational pieces about the developments and dangers of the newly dubbed “Atomic era.” One of the founders of the Bulletin was a biophysicist named Eugene Rabinowitch, who had worked on the Manhattan Project during World War II. Rabinowitch said that the aim of the Bulletin was to “awaken the public to the full understanding of the horrendous reality of nuclear weapons and of their far‑reaching implications for the future of mankind.”

In 1947, the Bulletin started to produce the Doomsday Clock, a way of measuring how close humanity was to destroying the world with man‑made nuclear weapons. When the first Doomsday Clock was released, the time was 11:53 PM (seven minutes to midnight). The furthest away the clock has been from midnight was in 1991, at the end of the Cold War between Russia and the US. The clock is presently at two minutes to midnight, the worst it has ever been, due to current concerning international stances of countries.

1 The Project Is Still Referenced In Popular Culture Today

The Manhattan Project has certainly not been forgotten more than 70 years after its completion. It is still referenced in many popular‑culture genres, essentially paving the way for an entirely new subgenre of nuclear destruction. The Manhattan Project has been featured in many television shows, movies, documentaries, pieces of fiction, music, art, and other forms of pop culture such as video gaming and board games.

Quickly following the close of the project, the film The Beginning or the End was released in 1947, which depicted an inaccurate and villainous story of how the atomic bombs were made. Many years later, the TV movie Day One provided a much more accurate portrayal of the project, going on to win an Emmy Award for Outstanding Drama. More recently, the Manhattan Project has been referenced in the Marvel Cinematic Universe in Iron Man, where the central character Tony Stark makes reference to his father helping the Manhattan Project.

Other portrayals include books such as Los Alamos by Joseph Kanon and The Wives of Los Alamos by Tarashea Nesbit. In 2014, a television series simply named Manhattan was produced for two seasons to critical acclaim before its cancellation in 2016. There have been and will continue to be many depictions of the project, as over 70 years later, we still find ourselves fascinated by the work conducted during the Manhattan Project.

When you set out on a top 10 history adventure through Lower Manhattan, you’re stepping into a living museum where every cobblestone, alleyway, and waterfront tells a tale of ambition, tragedy, and transformation. The modern skyline may dominate the horizon, but beneath the glass and steel lies a patchwork of stories that built the city we love today. Let’s walk the streets, dive into the archives, and uncover the ten most compelling chapters of this iconic district.

Why This Top 10 History Walk Matters

Understanding the layers of Lower Manhattan gives you a richer perspective on New York’s present, from its bustling markets to its hidden underground passages. Each stop on this tour reveals how immigrants, rebels, and ordinary citizens shaped a metropolis that continues to reinvent itself.

10 Collect Pond

The present‑day Columbus Park in Chinatown actually crowns what was once the city’s premier fresh‑water reservoir, known aptly as Collect Pond. Long before any skyscrapers pierced the sky, the Lenape people had a settlement hugging its banks, and in the 1540s the French erected a fortified trading post on a nearby island.

By the early 1700s, British colonists enjoyed the pond as a summer picnic spot and a winter skating rink. Yet the idyllic scene soon soured when tanneries moved in, turning the surrounding area—once called Mulberry Street—into the grimly nicknamed “Slaughterhouse Street.” By the 1800s, the water had become so polluted it was described as “a very sink and common sewer.”

In 1807 the city began digging what is now Canal Street, a canal intended to whisk the foul water away to the Hudson River. The rushed drainage left behind a marshy, mosquito‑infested landfill, upon which affluent slumlords erected tenements for a flood of poor immigrants seeking a fresh start.

9 The Five Points Slums

Partly built on the reclaimed, fetid ground of Collect Pond, The Five Points earned its name from a star‑shaped intersection where three streets converged: Anthony (now Worth), Cross (now Mosco), and Orange (now Baxter). The neighborhood’s layout formed a literal set of points, giving the area its memorable moniker.

Immortalized in Martin Scorsese’s 2002 film Gangs of New York, Five Points was notorious for its squalor. Tenements crowded together on unstable, poorly drained land, creating a breeding ground for cholera, tuberculosis, typhus, malaria, and yellow fever. The relentless influx of destitute newcomers provided slumlords with a steady stream of desperate tenants.

Crime ran rampant; the district was reputed to have the highest murder rate of any slum worldwide during the 19th century. Prostitution, gambling, and even rat‑fighting thrived in the cramped alleys. The area’s grim reality inspired Jacob Riis’s 1890 exposé How the Other Half Lives, which sparked sweeping reforms in sanitation, housing, and public safety throughout Lower Manhattan.

8 Castle Clinton

Before Ellis Island became the iconic gateway for immigrants, Castle Clinton served as the nation’s first official immigration processing center. Constructed amid rising tensions between the United States and Britain, the 28‑cannon fort was built on an artificial island off Manhattan’s southern tip and never saw combat during the War of 1812.

The site bears a dark early history. In the 1640s, after the Lenape refused to pay taxes imposed by Dutch settlers, the colonial governor allegedly ordered a gruesome retaliation—slaughtering men, women, and children and decorating Fort Amsterdam with their heads.

In 1815, the fort was renamed for outgoing mayor DeWitt Clinton, the visionary behind the Erie Canal that linked the Great Lakes to the Atlantic via the Hudson River. After its military relevance faded, the structure morphed into a beer garden, exhibition hall, opera house, and theater before becoming an immigration station in 1855.

The castle functioned as a processing hub until 1890, when operations moved to Ellis Island. Immigrants often fell victim to corrupt officials who swindled them or even died while awaiting entry. Today, the former island is filled in and attached to the mainland, and Castle Clinton stands at the southern end of Bridge Street, where guided tours are readily available.

7 Fraunces Tavern

If you’re craving a historic pint, step inside Fraunces Tavern at 54 Pearl Street, New York’s oldest bar. Established in 1719, the tavern originally bore the name Queen’s Head Tavern under the ownership of Samuel Fraunces.

During the Revolutionary War, Fraunces and his establishment played a covert role in a spy network that undermined British occupation of the city—a drama later dramatized in the TV series TURN: Washington’s Spies. After the war, George Washington hosted a farewell banquet for senior Continental Army officers at the tavern, coinciding with the British departure on Evacuation Day, November 25, 1783.

In 1789, Fraunces was appointed as President Washington’s first chief steward, overseeing the presidential household until his death in 1795. Modern scholarship now debates Fraunces’s racial identity, with many historians suggesting he may have been a free Black man, contrary to long‑standing portrayals.

Today, Fraunces Tavern operates as both a restaurant and a museum, showcasing artifacts from the Revolutionary era and preserving its legacy as a cornerstone of New York’s early social scene.

6 The African Slave Trade And Burial Grounds

While slavery is often linked to the American South, New York City ranked as the second‑largest slave‑holding metropolis in the British colonies during the mid‑18th century, trailing only Charleston, South Carolina.

The city’s most infamous slave market once thrummed at what is now Wall Street. Today, a sleek 42‑story condominium tower at 74 Wall Street sits atop the former site where enslaved people were bought and sold.

Slavery entered New Amsterdam in 1626, just two years after the Dutch first settled the area. Enslaved labor was crucial in constructing early defensive works, including the wall that gave Wall Street its name.

The only physical reminder of the market is a commemorative plaque installed in 2015. Nearby, the African Burial Ground Memorial stands as the oldest and largest excavated African burial site in North America. Discovered in 1989 during construction, archaeologists uncovered roughly 15,000 skeletons dating from the 1630s to the 1790s.

Because African Americans were barred from interring alongside whites, the burial ground became a mass grave for both free and enslaved individuals. Slavery was not fully abolished in New York until 1827.

5 City Hall Park

The green expanse surrounding New York’s City Hall is arguably the only sizable plot in Lower Manhattan that has never been wholly built over. Dutch settlers originally used the area as a public commons, but the British turned it into a venue for public executions after seizing the colony in 1664.

In 1775 the British began constructing a prison known as Bridewell. The outbreak of the American Revolution halted progress, leaving the unfinished structure—lacking even basic windowpanes—to become a grim holding place for hundreds of prisoners of war until the conflict ended.

Prior to the war, the grounds served as a rallying point for “Liberty poles,” wooden symbols erected to inspire rebellion and signal covert meetings of anti‑British conspirators. The Sons of Liberty would repeatedly raise these poles only to have British soldiers cut them down, creating a tense game of cat‑and‑mouse.

One notable clash occurred in January 1770 when patriots attacked British soldiers attempting to remove a liberty pole, sparking a skirmish on nearby Golden Hill—an event that predated the Boston Massacre by several weeks. In 1921, a 20‑meter‑tall replica of a sawed‑off liberty pole was installed to commemorate this revolutionary spirit.

4 The Catacombs At Old St. Patrick’s Cathedral

While Trinity Church’s graveyard at Wall Street and Broadway is famed for housing Alexander Hamilton’s tomb, a lesser‑known subterranean sanctuary lies beneath Old St. Patrick’s Church in modern‑day SoHo.

These catacombs offer a more immersive glimpse into the city’s burial customs. Constructed to protect the remains of affluent Catholic families from the rampant grave‑robbing of the 19th century, the underground chambers were an expensive privilege, reserved for the city’s elite.

Among the interred are members of the Delmonico restaurant dynasty and the man credited with introducing opera to New York. One particularly intriguing figure is Thomas Eckert, who served in multiple capacities—including presidential bodyguard—under Abraham Lincoln. On April 14 1865, Lincoln requested Eckert’s presence at a theater performance, but Secretary of War Edwin Stanton denied the request, a decision that remains shrouded in mystery regarding why Eckert was not beside Lincoln when he was assassinated that night.

3 Mob Hit Hunting In Little Italy

Although Little Italy’s footprint has shrunk dramatically—squeezed by Chinatown to the south and Nolita to the north—its streets still echo with tales of high‑profile mob violence.

At Umberto’s Clam House on Mulberry Street, notorious Colombo family hit man Crazy Joe Gallo celebrated his birthday on April 7 1972 with a family dinner. Mid‑meal, gunmen stormed the restaurant and opened fire, marking the first instance of a mobster being murdered in front of his own children.

Another infamous shooting took place in the late 1930s at the former ‘O Sole Mio’ restaurant, also on Mulberry Street. A grisly photograph of an unidentified victim sprawled on the pavement made headlines across the city. Today, the site houses a souvenir shop selling clichéd “I Heart NY” tees to unsuspecting tourists.

For those eager to delve deeper into organized‑crime history, the Museum of the American Gangster on St. Mark’s Place—just beyond Lower Manhattan’s borders—offers extensive exhibits on the era’s underworld.

2 The City’s Oldest Sites

New York is a city defined by constant change, yet only one structure from the 1600s still stands: a historic cemetery that serves as the final resting place for the city’s earliest Jewish settlers.

Located in today’s Chinatown, the burial ground contains 107 graves with remarkably legible headstones. The cemetery remained active through the American Revolution, holding the remains of several soldiers who fought in the conflict.

While Fraunces Tavern often claims the title of the oldest surviving building, many historians argue its numerous renovations disqualify it. Instead, St. Paul’s Chapel, erected in 1764, holds the distinction of being the oldest original structure still standing. The chapel even features a pew where George Washington knelt to pray on the day of his inauguration.

Nearby, the Edward Mooney House, completed in 1789, has worn many hats over the centuries—private residence, hotel, brothel, and saloon. At the turn of the 20th century, it became the headquarters of the flamboyant “mayor of Chinatown,” Chuck Connors, who led white tourists on “slumming” tours through Bowery bars and opium dens. Connors also helped future songwriting legend Irving Berlin secure his first gig at a local eatery.

Today, the building’s second‑floor façade proudly displays Chinese characters, a testament to Chinatown’s enduring presence in the city’s fabric.

1 Chinatown

Chinatown stands as the only substantial ethnic enclave remaining in Manhattan, outlasting once‑vibrant neighborhoods such as Harlem, Washington Heights, and especially Little Italy, which have all been eroded by gentrification.

First‑time visitors often find Chinatown both welcoming and overwhelming. The streets are lined with weathered yet delectable dumpling shops, expansive Eastern‑medicine pharmacies stocked with rows of herbal remedies, and bustling dim sum halls—including the massive 800‑seat Jing Fong, which feels more like a soccer field than a restaurant.

Chinese immigration to Lower Manhattan began in the 1870s. Facing discrimination not only from native‑born Americans but also from other immigrant groups like the Irish, Italians, and Germans, the Chinese formed tight‑knit communities. The 1882 Chinese Exclusion Act further limited new arrivals, reinforcing a sense of insularity.

Like other ethnic groups of the era, Chinese migrants organized gangs known as tongs, which ran opium dens, prostitution rings, and gambling establishments. Doyers Street, a narrow, elbow‑shaped alley, earned the nickname “Bloody Angle” after a violent tong battle left several gang members dead.

To evade law enforcement, the tongs utilized an intricate network of underground tunnels for smuggling and quick escapes. Today, a portion of this hidden passageway can be explored at Chatham Square’s Wing Fat Shopping Arcade, the last publicly accessible remnant of the subterranean labyrinth.

About The Author: Christopher Dale (@ChrisDaleWriter) writes on politics, society, and sobriety issues. His work has appeared in Daily Beast, NY Daily News, NY Post, and Parents.com, among other outlets.