Carlow Castle, now a ruin stands on the eastern bank of the River Barrow. It is thought to have been built by William de Marshal, Earl of Pembroke and Lord of Leinster between 1207 and 1213. Originally the castle was a rectangular block, containing the castle’s principal rooms protected by cylindrical towers at its corners. Today, tow battered towers and part of an intervening wall are all that remain after a local physician tried to remodel it as an asylum in 1814. In an effort to demolish the interior he placed explosive charges at its base and demolished all but the west wall and towers.