One of the most well-known urban legends of the 20th century? The widely reported UFO incident at Roswell, New Mexico. What started as the reported crash-landing of an unidentified object eventually led to an alleged cover-up and the birth of a supernatural story that’s been accounted many different ways and reinvented a small southwestern town into an enclave for alien enthusiasts. In the four-part series Expedition Unknown: Hunt for Extraterrestrials, Josh Gates investigates the mysterious event in New Mexico and even goes behind the scenes at the hangar where the wreckage is reported to have been briefly stored. While there is still so much that is unknown about the incident, here are six (mostly) irrefutable things to know about what happened in Roswell 70 years ago.

It Started with a Flying Object

In the summer of 1947, a flying object crashed near Roswell. Some observers reported seeing what appeared to be a flying disc, but the U.S. military released a statement to the press assuring the public that it was a weather balloon that crashed to Earth in early July. But William Brazel, a supervisor on the grounds where an object crashed outside of Roswell, said he gathered up the debris from the crash, which had crashed in June, not early July as the press statement had said.

There IS Evidence of Some Kind of Wreckage

The wreckage that Brazel the supervisor collected was about 5 pounds total, and included rubber; sticks; tough, glossy paper with a few letters printed on it; lightweight metals; fiber-optic cables; and tape. In 1947, many of these materials didn’t look like anything anyone had ever seen before. When Brazel called the town sheriff, Air Force personnel arrived to gather the materials. Some people in the area believed that the wreckage was from an alien spacecraft and that alien bodies were removed from the site to be studied, either at Area 51 in Nevada or in Roswell. After the military press release claimed the object as a rogue weather balloon, the story didn’t surface in national media again until a few decades later.

We Begin Seeing "Aliens"

Seventy years after the crash, most versions of the Roswell story include extraterrestrial beings on board the mysterious flying object. But only seven years after the incident, in 1954, the Air Force began conducting “dummy drops,” which involved anthropomorphic gray dummies fashioned to look like humans, dropped from high-altitude weather balloons. From a distance, these crash test dummies looked similar to the gaunt, waxy, green-gray figures that we often see in popular culture. In old news reports near Roswell, there are details about “disfigured” beings with only four fingers, perhaps accounting for the fact that the dummies were damaged from the falls. Over time, the Roswell UFO incident and injured "aliens" found in the desert would become associated in people’s collective memory, though the Roswell incident and the first dummy drop occurred seven years apart.

A Future President Reports a Possible UFO Sighting

In the 1970s, reports of UFO sightings were occurring across the United States and the world. One of the most notable reports was from then-Governor of Georgia Jimmy Carter, who reported seeing a suspicious, “self-luminous” aircraft in 1973, four years before he became the 39th President of the United States. A few years later during his presidential campaign in 1976, he was still so convinced he had seen a UFO that he promised to publicize all UFO-related knowledge, including what happened at Roswell, if he were to be elected to office. It was significant that among the many worldwide UFO reports in the '70s, even prominent politicians were claiming witness of unexplained flying objects, which gave more legitimacy to older incidents like Roswell. After President Carter was elected to office in 1977, he then stated that releasing any UFO-related knowledge would pose as a national security risk. The story behind the Roswell crash would remain unaddressed by the government for the next two decades.

The Government Gets Involved

In the 1990s, the security risk for exposing UFO sightings became clearer, as the world learned that there was a government cover-up at Roswell, after all. The government then stated that the flying object wasn't just an ordinary weather balloon, it was a nuclear testing balloon that was part of Project Mogul, a top-secret Air Forces project to use microphones on high-altitude balloons to detect Soviet atom bombs. High-altitude balloon technology had improved in the ’40s and the military had begun building wartime surveillance balloons using materials such as reflective foil, lightweight sticks and fiber optic cables. These were all new and otherworldly-looking materials that Brazel had found decades before that didn't seem to fit the bill for a run-of-the-mill weather balloon. Despite the newest government statement, reports of UFO sightings that range from seeing strange aircraft formations in the night sky to an unexplained flying object seen by NASA astronauts in outer space (that turned out to be a satellite) kept occurring at the same rate as it did in the ’70s.

UFOs are Everywhere in Roswell Today

The alien culture and celebration in Roswell lives on, even as the story was debunked. Every year, Roswell is home to a large festival to commemorate and celebrate the crash landing with costume parades for people and pets, live entertainment, guest speakers, and family-friendly activities. This year, the festival celebrated the 70th anniversary of the UFO incident. Further up the road in Roswell, you can find a flying saucer-shaped McDonald’s restaurant, an international UFO museum and research center, and UFO tours to the Project Mogul balloon crash site.

Roswell's Alien Influence Lives on in Pop Culture

The series of events in Roswell led to a surge of aliens, UFOs and extraterrestrial beings in pop culture for decades to come, including the hit science fiction TV show Roswell from 1999-2002, which followed a group of alien-human hybrid teenagers with supernatural powers in Roswell, New Mexico. The film Roswell: The UFO Cover-Up came out during the same time period in 2001, starring Kyle McLachlan and Martin Sheen.

Step further into alien folklore and the Roswell mystery with Expedition Unknown: Hunt for Extraterrestrials, beginning Oct. 4 at 9|8c.