The design includes a partially retractable roof. A signature feature of the stadium, following on from the old Wembley's distinctive Twin Towers, is the 134 metres (440 ft) high Wembley Arch. With a span of 317 metres (1,040 ft), this steel arch is the longest single span roof structure in the world and, uniquely for a stadium, requires beacons for low flying aircraft. The 90,000-capacity venue is the second largest stadium in Europe, and serves as England's national stadium. The stadium roof has an area of 40,000 m2, of which 13,722 m2 is movable. The primary reason for the sliding roof was to avoid shading the pitch, as grass demands direct sunlight to grow effectively. The sliding roof design minimises the shadow by having the roof pulled back on the east, west and south. One of the aims was for the pitch to be in sunlight during the match between the beginning of May and the end of June, between 3pm and 5pm, which is when the FA and World cups would be played.