At the time San Francisco International Airport opened as Mills Field Municipal Airport of San Francisco in 1927, most of the San Francisco Peninsula was pastureland. Over the years, new terminals and hangars were built to satisfy the demand of increased air traffic. Beginning with a small administration building of residential character including horizontal wood siding and red cedar shingles, the airport advanced to the larger San Francisco Airport Administration Building. After continuous growth, in 2000 the airport was reorganised and expanded into the vast, structurally iconic new International Terminal. The new building acts as a gateway between land and air, offering a recognisable image to arriving and leaving passengers. It is organised over five levels, making it America's first mid-rise terminal. It receives multiple modes of transportation -- linking cars, busses, the Bay Area Rapid Transit (BART) system and the internal light-rail system. According to Craig Hartman, design architect with SOM, the terminal is "founded upon the qualities of light and lightness". He says of the new roof: "We conceived of it as a floating, sheltering plane and as a symbol." The building's position above several lanes of traffic required a 380-foot long span between the central columns -- essentially the building is a bridge. Thus the building itself is in a state of lift-off, offering the first step into the air for departure or a transition space for arrival before the traveller really gets back to the ground. The terminal is built on friction-pendulum base insulators that allow it to swing in the event of an earthquake. The roof trusses' shape evokes many possible associations, the rolling Bay Area hills, the wings of airplanes, a bird in flight -- all images not unusual inspirations for airport designs, though in this case especially elegantly achieved.