Many amphitheaters built in the early part of the 20th century — like the Hearst Greek Theatre in Berkeley which opened in 1903 or LA's Greek Theatre which opened in 1930, relied on design and amplification principles dating back to Ancient Rome, with audiences packed in tightly and elevated above a central stage. But the popularity and power of the Grateful Dead in the 1970s and the success of two amphitheater projects in Northern California (the Shoreline Amphitheater in Mountain View and the Concord Pavilion) by rock pioneer and promoter Bill Graham led to a building boom across the country. Through much of the 1980s and early 1990s, Promotion companies like Cellar Door Entertainment and Pace Concerts raced to build inexpensive outdoor amphitheaters on unused property.