At its base is a porte-cochère within four equilateral pointed arches, the north of which frames the main entrance of the Centre Block, and the jambs of the south adorned by the supporters of the Royal Arms of Canada. Near the apex, just below the steeply pitched roof, are the tower's 4.8 m (16 ft) diameter clock faces, one on each of the four facades. The mechanical workings of the timepiece were manufactured by the Verdin Company and are set by the National Research Council Time Signal. One level below, running around the circumference of the tower's shaft, is an observation deck. This was the highest accessible space in Ottawa until the early 1970s; the Peace Tower dominated the Ottawa skyline, as a strict 45.7 m (150 ft) height limit was placed on other buildings. That limit, however, was later rescinded, leading the Peace Tower to lose its distinction as the city's tallest structure. Cantilevered out at each of the four corners of the tower, at the level of the observation platform, are four 2.5 m (8 ft 4 in) long, 75 cm (2 ft 6 in) high, and 45 cm (1 ft 6 in) thick gargoyles made of Stanstead grey granite from Beebe, Quebec.