the individual Knights of the Thistle, carved by Grinling Gibbons. However, in 1688, following the Glorious Revolution, the Edinburgh mob broke into the abbey, entered the Chapel Royal and desecrated the royal tombs. The association of the church with these events and the absence of a royal court left the building out of public interest. The ageing timber roof trusses were replaced by stone vaults and outer stone slabs in 1758-60 by the architect John Douglas and the stonemason James McPherson. However this proved to be a disastrous change. The excessive weight of the stone could not be supported by the walls. The strength of stone vaults depends on the containment of their thrusts, which the decayed flying buttresses could not contain any more, and a small movement (less than 1/30 of the span) can cause severe deformation and collapse. It took six years for the deformation to become alarming. This forced the Barons of the Exchequer (the administrators of the Palace) to close the church on safety grounds in 1766, following inspection by William Mylne. On 2 December 1768 the roof collapsed in two stages, leaving the abbey as it currently stands, a roofless ruin. The restoration of the abbey has been proposed several times since the 18th century – in 1835 by the architect James Gillespie Graham as a meeting place for the General Assembly of the Church of Scotland and, in 1906, as a chapel for the Knights of the Thistle – but both proposals were rejected. In July 1829, the ruins of the Holyrood Chapel were visited by Felix Mendelssohn. Holyrood, as Mendelssohn related to his family in a letter, served as inspiration for his Scottish Symphony. List of Abbots (derived from Grant's "Old and New Edinburgh") Alwyn (d. 1155) author of "Book of Homilies and Epistles" Osbert (d. 1150) William I, built a wall around the abbey Robert, who helped to found the new burgh of Canongate John, who campaigned to move the monastery from Edinburgh Castle to the Abbey William II (1206) Walter (d. 1217), Prior of Inchcolm Abbey abbot from 1209 William III William IV, son of Owen, resigned 1227 to become a hermit on Inchkeith but returned later as a monk Elias I, son of Nicholas, drained the marsh behind the abbey Henry of Holyrood, left in 1253 to become Bishop of Galloway Radulph Adam (or Alexander) a "traitor" who paid homage