three-bay transepts with a central tower above, and an eight-bay aisled nave with twin towers at its west front. Some scholars believe the high vaults to be sexpartite (though this is not clearly supported by the 17th century illustrations of the interior). Such a design was probably archaic in that period, and difficult to execute or maintain. Evidence of the construction qualities of the stonemasons has remained on the S aisle vaults, which are set on an almost square plan of 4.4 m (14 feet), but built relatively roughly, with thin flagstones and not much attention to keeping the vertices straight. They were probably plastered, with exposed thin ribs. Among the chief benefactors of Holyrood during the four centuries of its existence as a religious house were Kings David I and II; Robert, Bishop of St. Andrews; and Fergus, Lord of Galloway. Around the abbey was a five-mile area of sanctuary, taking in much of Holyrood Park, where debtors and those accused of crimes could appeal to the Bailie of Holyroodhouse for protection. Brass sanctuary stones mark the boundary of the sanctuary on the Royal Mile. Those granted sanctuary would be given lodgings in the buildings around the abbey and obtained the nickname 'Abbey Lairds'. The Parliament of Scotland met at the abbey in 1256, 1285, 1327, 1366, 1384, 1389 and 1410. In 1326, Robert the Bruce held parliament here, and there is evidence that Holyrood was being used as a royal residence by 1329. The Treaty of Edinburgh–Northampton (1328), which ended the First War of Scottish Independence, was signed by Robert I in the "King's Chamber" at Holyrood in March 1328. The abbey's position close to Edinburgh Castle meant that it was often visited by Scotland's kings, who were lodged in the guest house situated to the west of the abbey cloister. In the mid-15th century, with the emergence of Edinburgh as the main seat of the royal court and the chief city in the kingdom, the Kings of Scots increasingly used the accommodation at Holyrood for secular purposes. James II and his twin brother Alexander, Duke of Rothesay, were born there in October 1430. James was also crowned at Holyrood in 1437 and building works were carried out before his marriage there in 1449. Between 1498 and 1501, James IV constructed a royal palace at Holyrood, adjacent to the abbey cloister. The Abbey refectory was converted into a