After the battle of Hastings, William the Conqueror marched upon London, but was opposed by a body of the citizens in Southwark, whom he repulsed; but recognising their valour and perceiving the strength of the City's fortifications, he went to subdue the Western Counties, and his success in that direction showed the Londoners that the wisest and most politic course would be to submit; when the Norman duke entered the City, and was presented with the keys and acknowledged as King of England. He was no sooner in possession of the City than he caused three castles to be erected, ostensibly for the protection of the City, but really to overawe the inhabitants. These were the Tower at the eastern, and Baynard and Montfichet Castles at the western, extremity of the walls. The Tower became the residence of the Norman kings, and Baynard Castle that of the chatelain and standard-bearer of the City—offices held first by the Baynards, and afterwards by the Barons Fitzwalter. Montfichet Castle was destroyed by fire in the reign of William, and the Black Friars' Monastery built on the site—the best of the stones being used in the re-edification of St. Paul's Cathedral, which had been destroyed by fire. Fitzstephen speaks of the walls being "both high and thick, with seven double gates," which appear then to have been in good condition, although the south wall had been "subverted and carried away by the tide." But very soon after some portions seem to have fallen into a ruinous condition; as Roger of Wendover and Matthew Paris tell us that the barons, when in arms against King John, in 1215, entered the City by Ealdgate, and demolished the houses of the Jews, to obtain materials wherewith to repair that gate and the adjoining walls. In 1257, also, it is stated, Henry III. "caused the walls, which were greatly decayed, and destitute of towers and turrets, to be repaired in a handsomer manner than before, at the common charge of the City."