The California Gold Rush of 1849 brought a sudden flood of ship traffic into San Francisco Bay, and the need for navigational aids became urgent. Congress appropriated funds for a string of lighthouses along the Pacific Coast, and Alcatraz -- sitting in the middle of the bay's main shipping channel -- was the obvious first location. The original lighthouse, a Cape Cod-style cottage with a lantern on its roof, began operation in 1854 with a third-order Fresnel lens. It guided ships past the rocky island and through the currents that sweep through the Golden Gate, currents that have claimed vessels since the first European explorers entered the bay.

By the early 1900s, the military prison facilities being constructed on Alcatraz had grown tall enough to block the lighthouse beam from certain angles. The solution was a new, taller lighthouse -- the 84-foot concrete tower completed in 1909 that still stands today near the southern tip of the island. The original lighthouse was demolished. The new tower's automated light and foghorn continue to serve maritime navigation, marking the island for ships that pass through the bay's central channel. The lighthouse's location at the southern end of the island means visitors arriving by ferry see the light tower first, before the prison cellhouse comes into view.

The lighthouse's priority in Alcatraz's timeline deserves emphasis. The island served as a military fortification in the 1850s, a military prison from the 1870s, and the infamous federal penitentiary from 1934 to 1963. The lighthouse predates all of these uses except the earliest fortification. It has been operational, in one form or another, for over 170 years -- far longer than the 29 years of the federal prison that made Alcatraz famous. The light still sweeps across the bay waters every night, a reminder that the island's primary purpose was always navigation, not punishment.