During the first century of the British period, the square was used for military parades by the garrison and therefore known as the "Parade" or "Grand Parade". In 1704, after the city's capture by an Anglo-Dutch fleet, the British converted the hospital and chapel of "La Santa Misericordia" into a debtors' prison. In 1753, a survey of Gibraltar went on showing a prison at the western end of the square. After the Great Siege, a colonnaded Georgian guardhouse was built on the southern side of the square. It was the "Main Guard", the place from which all the sentries in Gibraltar were posted each evening. Some years later it hosted the Fire Brigade. After the move of the brigade to the new fire station at Victoria Battery in 1938, it became the "Rates Office". Today the guardhouse houses the Gibraltar Heritage Trust.