compared the concept to a tree. The idea was that although the national pavilions were like individual flowers they needed to be connected to the whole via branches and a trunk. Thus the Symbol Zone became the trunk and the moving pedestrian walkways and sub-plazas became the branches. These elements were reinforced with colour, with the trunk and branches in plain white and the pavilions in their own colours that were determined by the national architects. The Symbol Zone ran north–south across the site, spanning an arterial road running east–west. The Festival Plaza was to the north of road and had the main gate on its southern end. To the north of the main gate and central to the Festival Plaza was the Tower of the Sun from which visitors could join pedestrian walkways that travelled out towards the north, south, east and west gates. The Theme Space under the space frame was divided into three levels, each designed by the artist Tarō Okamoto, The underground level represented the past and was a symbol of the source of humanity. The surface level represented the present, symbolising the dynamism of human interaction. The space frame represented the future and a world where humanity and technology would be joined. Tange envisioned that the exhibition for the future would be like an aerial city and he asked Fumihiko Maki, Noboru Kawazoe, Koji Kamiya and Noriaki Kurokawa to design it. The Theme Space was also punctuated by three towers: the Tower of the Sun, the Tower of Maternity and the Tower of Youth. To the north of the Theme Space was the Festival Plaza. This was a flexible space that contained a flat area and stepped terrace. The plaza could be rearranged to provide for different requirements for seating capacity, from 1500 to 10000. The flexibility extended to the lighting and audio visual equipment allowing for a range of musical performances and electronic presentations. Festival Plaza was covered by the world's first large-scale, transparent membrane roof. It was designed by Tange and structural engineer Yoshikatsu Tsuboi + Kawaguchi & Engineers. Measuring 75.6 m in width and 108 m in length, it was 30 m high and supported by only six lattice columns. Seventy-seven countries participated in the event, and within six months the number of visitors reached 64,218,770, making Expo '70 one of the largest and best attended expositions in history. It held the