modern domed stadium built in Houston, Texas, in 1965. The largest previous covered sports arenas provided only limited performing space and seated no more than 20,000 persons. The Astrodome, however, built on the principle of the dome, completely protects a sports area suitable for baseball and American football, with seating for 66,000 spectators in six tiers. The plastic-paneled dome, spanning 642 feet (196 metres), is supported by a steel lattice; the entire interior is air-conditioned at 74 °F (23 °C) and fully lighted with power from its own electric-generating system.