They are the 165-foot-tall towers that support outdoor lighting for parts of Austin. Thirty-one of these metal giants were erected in 1895 using electricity from Austin's first power plant on the Colorado River. The towers first used carbon arc lamps that were lit nightly by a worker who got to the top in an elevator that runs up the center of the framework. These were replaced in the 1920s by incandescent lamps and then by mercury vapor lamps in 1936. There are 17 towers in use today. A replica of a moonlight tower serves as the center post for the Zilker Park "Christmas Tree" of lights each year.