For the greater part of its length, houses were built completely over the bridge, leaving only three vacancies, one an open space called the Square, not far from the city, and another at the Southwark end where the drawbridge was. The thoroughfare passed through the centre of the bridge beneath the houses, forming a kind of tunnel with shops on either side. As there was no footway, it was the safest and most usual custom to follow a carriage which might be passing across. The practice of erecting houses on bridges frequently prevailed in early times, the object doubtless being to secure property for the maintenance of the bridge. In many instances, too, a chapel was added. A curious instance of this custom was on the bridge at Droitwich, where the road passed through the chapel, and separated the congregation from the reading-desk and pulpit. Another famous bridge chapel was erected over the river Calder at Wakefield. London Bridge had a beautiful chapel dedicated to St. Thomas of Acon, and consisting of two floors, the upper being on a level with the Bridge road, and the lower only slightly above the level of the river, its apartment occupying the interior of the chapel pier. Another notable building was the Bridge Gate or Tower, situated at a distance of about one-third of the length from the Southwark end, and forming the boundary limit between the City and that borough. Adjoining it on the Surrey side was the drawbridge, which could be lowered for the passage of vessels up the river, and for defence of the City from the south in times of invasion. Another tower stood almost at the entrance into Southwark, on the second pier. Here, in 1263, Simon de Montfort forced a passage into the city. In 1471 the Kentish Mariners, under the bastard Falconbridge, burnt the gate, and some fourteen houses on the bridge. Sir Thomas Wyatt, in 1554, was repulsed, after a determined attack on the bridge and its defenders; not, however, before he had attacked the Bishop of Winchester's palace at the bridge foot, and cut to pieces all his books, "so that men might have gone up to their knees in the leaves so torn out." Over this tower the traitors' heads were fixed in the sixteenth century, having been removed from the Gate Tower, north of the drawbridge. These gates were decorated with leafy boughs and garlands of flowers on Midsummer Day. On the west wall, set up in 1492, was a statue of the patron and supposed guardian of the bridge and City, St. Thomas of Canterbury.