By the Tudor period, there were some 200 buildings on the bridge. Some stood up to seven storeys high, some overhung the river by , and some overhung the road, to form a dark tunnel through which all traffic had to pass; this did not prevent the addition, in 1577, of the palatial Nonsuch House to the buildings that crowded the bridge. The available roadway was just wide, divided into two lanes, so that in each direction, carts, wagons, coaches and pedestrians shared a single file lane wide. When the bridge was congested, crossing it could take up to an hour. Those who could afford the fare might prefer to cross by ferry, but the bridge structure had several undesirable effects on river traffic. The narrow arches and wide pier bases restricted the river's tidal ebb and flow, so that in hard winters, the river upstream of the bridge became more susceptible to freezing and impassable by boat. The flow was further obstructed in the 16th century by waterwheels (designed by Peter Morice) installed under the two north arches to drive water pumps, and under the two south arches to power grain mills; the difference in water levels on the two sides of the bridge could be as much as , producing ferocious rapids between the piers resembling a weir. Only the brave or foolhardy attempted to "shoot the bridge" – steer a boat between the starlings when in flood – and some were drowned in the attempt. The bridge was "for wise men to pass over, and for fools to pass under."