Archaeologists have made an amazing discovery beneath the surface of Alcatraz – and they didn’t need to dig a single trench.

Image: Pascale BEROUJON/Gamma-Rapho via Getty Images

Timothy de Smet and his team of archaeologists from Binghamton University are using hi-tech equipment on a fascinating project. Using non-destructive methods, they’re exploring the ground beneath the former exercise yard at the notorious Alcatraz Federal Penitentiary. And what their investigations ultimately reveal comes as a complete surprise…

We’ll return to de Smet and the finds that he made, but first let’s find out more about Alcatraz. The island itself is located in the waters of the bay of San Francisco and sits just over a mile from the Californian city. It’s basically a rocky outcrop measuring just over 1,700 feet long and 580 feet at its widest point.

In addition, Alcatraz – which is sprawled over 22 acres of land – boasts two high points: one rising to 135 feet from the surface of the bay and the other reaching 138 feet. And a Spaniard, Juan Manuel de Ayala, gave the first written account of the island in 1775. He called it La Isla de los Alcatraces, or the Island of the Pelicans, although some sources suggest that the last word should be translated as “gannets” instead. In any case, the name by which we know the island today has been derived from de Ayala’s writings.

The Spanish also went on to construct some small buildings on the island, although they don’t appear to have made any significant efforts to settle what was, after all, no more than a barren rock. But it turns out that even a barren rock can have an owner, as Alcatraz’s first recorded proprietor was one Julian Workman. When Workman was in charge of the land, however, it was Mexican territory.

Workman, a ranch owner, was given the island in 1846 by Alta California governor Pio Pico, and he apparently committed to establishing a lighthouse there. Yet it appears that such a building never materialized. Instead, John C. Frémont, California’s military governor, bought the rocky outcrop for $5,000 for the U.S. later that year.

And nothing much appears to have happened on the island for a few years following Frémont’s purchase. After the war with Mexico ended in victory for the U.S in 1848, however, the land officially became U.S. territory. You see, one of the stipulations of the resulting Treaty of Guadalupe Hidalgo was that California would cease to belong to Mexico. After that term was agreed upon, then, the state – including Alcatraz Island – became definitively American.

Then, in 1850, the Americans made a decision about their island possession. In particular, the U.S. president of the day, Millard Fillmore, ordered that Alcatraz be given over to military use. This effectively turned the outcrop into a military base, and the island would subsequently serve as a defensive position for the Bay of San Francisco.

And Frémont – the man who had paid the Mexicans $5,000 for the island – reportedly expected to make a killing from his investment. This, he apparently believed, would come in the shape of a handsome cash payment from the American government. After all, in order to take over the island for military purposes, the authorities would have to show their gratitude to Frémont – or so he assumed.

But the U.S government had a strategy to avoid paying any amount of money to Frémont for the island: in short, it simply declared that the man’s purchase of the territory from Mexico was invalid. And as a consequence, Frémont was given precisely zero in exchange for Alcatraz. Undeterred, the rancher and his successors subsequently fought the government through the courts right up until the 1890s; in the end, though, they still received nada.

Yet despite President Fillmore’s 1850 order that the military take over Alcatraz, three years would pass before construction began on the island. In 1853 the U.S. Army Corps of Engineers started work under the command of the splendidly named Zealous B. Tower, who went on to fight as a Unionist general in the Civil War.

And the sudden decision to fortify Alcatraz had a specific reason: the California Gold Rush of 1848. People were coming to the state from all over the world, you see, drawn by the prospect of getting their hands on the precious yellow metal. In only a matter of years, then, San Francisco grew from little more than a hamlet of some 300 people to a city with a population of 30,000.

So, in the eyes of the U.S. government, San Francisco Bay needed a defensive strategy – with part of that plan being the fortification of Alcatraz. To complete the defense of the bay, a stronghold would also be built on the nearby island of Fort Point. However Alcatraz was not only ready first, but it was also the island with the strongest fortifications.

Image: Survey HABS CA-1792 via Library Of Congress

Indeed, a Pacific Coast Board of Engineers report from 1852 surmised, “Nature seems to have provided a redoubt for this [military] purpose in the shape of Alcatraz Island. Situated abreast the entrance directly in the middle of the inner harbor, it covers with its fire the whole of the interior space lying between Angel Island to the north, San Francisco to the south and the outer batteries to the west.”

What’s more, Tower and his men set about their work on Alcatraz with gusto. Using the island’s natural topography to their advantage, the team broke up rocks and built walls to give the island a defense all along its coast. Guns were then positioned around the perimeters facing west, south and north. In addition, some 111 mighty cannons called columbiads dotted the island.

Structures called caponiers – stone towers projecting from the shores of Alcatraz – were also positioned in between the columbiad emplacements. And each of the caponiers was armed with a howitzer – a cannon somewhat smaller than a columbiad. Anyone with a mind to seize this island, then, would certainly have a formidable task on their hands.

In addition, a heavily defended barracks – called the citadel – was erected on one of the high points next to a lighthouse. This beacon had been built in 1854 and was in fact the first navigational light to be positioned on the U.S. Pacific Coast. The original tower was then replaced by a new one in the early 20th century – and that is the one you’ll see if you visit the island today.

The citadel’s defenses, meanwhile, included a moat with a drawbridge, windows specially adapted for infantrymen to fire their rifles from and a battery of howitzers. The barracks was designed to house 100 men, although this could be increased to 200 if Alcatraz was assaulted. And should a siege occur, the fortress had enough supplies to last the occupants for four months.

Nevertheless, it took until 1859 to complete the fortification of Alcatraz – largely thanks to a shortage of labor. After all, many of those who arrived in San Francisco during the gold rush did not have construction work on their minds; instead, their ambitions lay in the prospecting fields. And the building difficulties were compounded by the fact that quantities of granite had to be brought in from China.

Then in 1861 – not long after the completion of the Alcatraz fortress – the U.S. Civil War broke out. And the commander of the island at the time, one Colonel Albert Johnston, was, in fact, a Southerner. Despite Johnston’s roots, though, he stayed loyal to his Federal masters until he resigned his post. The colonel then joined the Confederate Army and died in action at the Battle of Shiloh.

Yet while the island’s garrison ultimately took in more than 350 men, it never actually came under attack during the Civil War. And while there had been a Confederate plot to assault Alcatraz, this never came to pass. Instead, in 1863 three co-conspirators were jailed after the captain of the ship involved boasted about the plan in a bar. The three detainees were then sentenced to ten years each, although a generous President Lincoln eventually afforded them all pardons.

Of course, Alcatraz is now more famous for its role as a prison location than as a military fortress. And in fact there is a long history of incarcerating people on the island; soldiers who had gotten on the wrong side of the law were locked up there from 1859. Alcatraz also served as a holding base for Confederate prisoners during the Civil War.

However, it was not until 1934 that Alcatraz hosted a federal penitentiary for civilians. And thanks to its geography, the island was an obvious place to imprison criminals. Surrounded by freezing waters that are agitated by powerful currents, the stretch of land is an extremely difficult – if not impossible – place from which to escape successfully.

Image: George Rinhart/Corbis via Getty Images

But before a federal prison ever stood on the island, the military increasingly used Alcatraz as a home for the incarcerated. This shift of purpose from defensive base to prison began, it seems, in 1867 with the construction of a purpose-built jailhouse. And during the Spanish-American War of 1898, the jailed population on Alcatraz soared from just 26 to more than 450.

Then, in 1909, the construction of a large concrete cell building further cemented Alcatraz’s reputation as a prison island. Finished in 1912, the block is still the largest structure on the island today. Finally, in 1933, the military authorities decommissioned their disciplinary barracks and handed it over to the Prisons Bureau.

And the first federal prisoners – 137 of them – arrived at Alcatraz Island on the morning of August 11, 1934. Yet these men were not just any old criminals; instead, the authorities had hand-picked agitators who had disrupted life at other federal prisons. These convicts had then traveled from United States Penitentiary, Leavenworth to Alcatraz by train under a guard of 60 – a group that included U.S. Marshals and FBI agents.

At the prison, 155 guards met the criminals, who were mainly murderers and bank robbers. The warden in charge, meanwhile, was James A. Johnston – a man with a reputation as a strict disciplinarian. And given the nature of the men who spent time on Alcatraz, Johnston’s work – as well as the jobs of his guards – may have been far from easy.

Image: Chicago Bureau (Federal Bureau of Investigation) – Wide World Photos

Furthermore, the list of men who spent at least part of their sentences at Alcatraz almost reads like a who’s who of infamous American criminals. George “Machine Gun” Kelly, Al Capone and Alvin “Creepy” Karpis all spent time on the island, for example. Karpis was one of only four criminals to have been named by the FBI as “Public Enemy Number One” as well as the only member of the nefarious quartet to have been captured alive.

And as we pointed out earlier, Alcatraz became a prison location because the island’s geography made it nigh-on impossible to flee successfully to the mainland. But that didn’t stop some of the criminals incarcerated there from trying. During Alcatraz Federal Penitentiary’s 29 years as an operational prison, there were 14 attempts at escape involving 36 prisoners.

Of those 36 would-be escapees – two of whom tried twice – 23 were recaptured alive, six were gunned down, five are categorized as “missing and presumed drowned” and two actually drowned. The prison authorities therefore claimed that no one ever got out alive. But, obviously, that handful of “presumed drowned” prisoners does leave room for speculation.

Image: Michael Esslinger via Alcatraz Cruises

Two of the five allegedly drowned fugitives were Ralph Roe and Theodore Cole, who got off the island in 1937 in the second of the 14 escape attempts. There was a storm when they absconded, however, making San Francisco Bay even more treacherous than usual. Consequently, most experts believe that the men got swept up in the currents and ultimately met their deaths.

Perhaps the most intriguing escape attempt, though, was the 13th, which took place in June 1962. On that occasion, Frank Morris and Clarence and John Anglin fled the prison in an elaborately planned operation, with none of their bodies later surfacing. And in 2013 the city’s police received a letter purportedly written by John Anglin that claimed all three men had survived their ordeal. Did Anglin really write the letter? We may never know for sure. The men’s alleged breakout, however, was immortalized in the Clint Eastwood flick Escape from Alcatraz.

Not long after the trio’s attempt, however, the Alcatraz Penitentiary shut down for good. So, it’s time to get back to Timothy de Smet and his Binghamton University archaeological team. In 2018 the group surveyed the former prison’s exercise yard, looking at what was beneath the floor. The researchers did this by using radar equipment that could “see” below the surface of the ground in conjunction with laser scans of the area.

This non-invasive technique therefore meant that there was no need to dig trenches. And what the team’s research revealed to be hidden from view beneath the surface of the prison yard was truly surprising. You see, the archaeologists came across remarkably intact structures dating back to the time when Alcatraz was a military fortress.

Under the exercise space, the team found what a January 2019 Binghamton University website article called “a ‘bombproof’ earthwork traverse.” Beneath that was a vaulted tunnel of brick construction complete with ventilation shafts. And what amazed de Smet was the well-preserved condition of these remains.

In the website article, de Smet is quoted as saying, “I was surprised [about the discovery] for several reasons. The remains of these historical archaeology features were just beneath the surface, and they were miraculously and impeccably preserved. The concrete veneer of the recreation yard floor is incredibly thin and, in fact, in places sitting directly atop the architecture from the 1860s.”

“We also learned that some of the earthwork traverses were covered over with thin concrete layers through time – [most] likely to decrease erosion on the rainy, windy island,” de Smet continued. “It was wonderful to find the history just beneath our feet that we can visualize for the public.” In addition, he explained that when Alcatraz Federal Penitentiary was built atop the old 19th-century fort, there was little consideration for the heritage value of the military installation.

But despite the wholesale destruction of the fort, de Smet wondered what may still lie underneath the prison. “As such, we sought non-invasive, non-destructive means to ascertain if any historic archaeological remains lay beneath several parts of the island, like the recreation yard of the infamous penitentiary. We did not know what to expect,” the archaeologist pointed out.

And de Smet also explained the thinking behind the hi-tech methods that his team had used to explore beneath the surface of the Alcatraz recreation yard. “With modern remote-sensing methods like these, we can answer fundamental archaeological research questions about human behavior, social organization and cultural change through time without costly and destructive excavation.” he said.

Plus, De Smet also described the groundbreaking significance of these modern methods of archaeological research. For one, the incredible finds that the Binghamton team made during this investigation proved archaeology could be completely non-invasive. There was now no need to destroy buildings above the surface to discover what lay below them. Remote sensing was all that was need to get the job done.

Of course, it’s nearly 60 years since any prisoners occupied the cells at Alcatraz. Today, curious explorers can visit the ill-famed prison, as it is part of the Golden Gate National Recreation Area. And as visitors walk over the exercise yard, they may do so in the knowledge that the remains of a historic 19th-century military base lie beneath their feet.