Inhospitable and inescapable, the legendary Federal Penitentiary on Alcatraz Island played host to some of the most notorious criminals of the 20th century. Originally conceived as a concentration program to manage the most difficult prisoners in the federal penal system, the isolated and harsh environment of "The Rock" became a symbol of cold, impersonal justice, earning the prison its infamous nickname.

This specimen is a large piece of concrete salvaged by the National Park Service during restoration of the site. These specimens vary in shape and size and are sold individually.

In some pieces, indentations and rust from steel bars can be clearly seen in the concrete. Each also comes with a certificate of authenticity.

""It looks like Alcatraz has got me licked." - Gangster Al Capone

The actual bedrock of the 22-acre Alcatraz Island is called greywacke.  This sandstone melange was laid during the Cretaceous and is part of a geologic terrane which includes most of the City of San Francisco including Nob, Russian, and Telegraph Hills.  During the Pleistocene Epoch, the San Francisco Bay was free of water, and what is now the Sacramento River ran through the Golden Gate to the sea.  The course of this river can still be traced on the floor of the bay as it winds around Alcatraz and nearby Angel Island.

According to native histories, the island was actually a place of exile in ancient times and served as a place of refuge when the first Spanish came to the area. One such spaniard would give the island its now iconic name. Naval officer Juan Manuel de Ayala y Aranza passed through the Golden Gate in August of 1775, charting the features and making contact with local Native American tribes. He gave names to many features, including a sandstone island so densely populated with brown pelicans he named it La Isla de los Alcatraces, or "The Island of the Pelicans," a name which stuck when the United States took possession of the island in 1846.

Fearing that foreign interests might try to take control of the suddenly valuable region, President Millard Fillmore signed an order in 1850 placing Alcatraz Island, as well as several others in the bay, under the control of the U.S. Army and directing the construction of defensive fortifications.

While the gun batteries of Alcatraz fortress were never called upon to defend the city, the remote nature of Alcatraz made it an ideal location for holding military prisoners.  Confederate soldiers and sympathizers were housed here during and after the Civil War, as were so-called "rebellious" Native Americans.  During the Spanish-American War, the incarcerated population of Alcatraz soared into the hundreds, leading to more construction.

After a fire destroyed the wooden citadel, construction began on what would become the world's largest reinforced concrete building.  Completed in 1912, this 600 cell structure would house conscientious objectors during World War I and eventually become the foundation for the U.S. Federal Penitentiary known as "The Rock".

 Originally conceived as a concentration program to manage the most difficult prisoners in the federal penal system, the isolated and harsh environment of "The Rock" became a symbol of cold, impersonal justice, earning the the prison its infamous nickname.

In all, some 1,545 men were incarcerated at Alcatraz, including famous Chicago gangster Al Capone, James "Whitey" Bulger, George "Machine Gun" Kelly, and Robert Stroud, also known as "The Birdman of Alcatraz".  Over the course of 29 years, only 36 inmates attempted to escape Alcatraz.  Officially there were no successful escapes, however, in the early hours of June 12th, 1962, Frank Morris and brothers Charles and John Anglin slipped into the San Francisco Bay in a makeshift raft crafted from stolen raincoats.

The trio worked for six months to widen the ventilation ducts inside their cells and then escaped through a utility corridor behind their cellblock.  Fragments of their personal belongings as well the remains of their raft were discovered but the prisoners bodies were never recovered.

Ironically, the men were aided in part by the very construction which set Alcatraz apart when it was completed in 1912.  Back then, Alcatraz was a military prison and the new cellblock was the largest reinforced concrete building in the world.  After decades of exposure to the salty, cold winds of the San Francisco Bay, airborne chlorides penetrated the concrete and degraded the reinforcing steel.  This was further exacerbated by the atmospheric carbon dioxide which had carbonated the concrete and caused further corrosion.

Less than a year after the 1962 escape, Attorney General Robert F. Kennedy ordered the prison closed.