 Complete the following phrase:  During the 15th century the castle was increasingly used as an arsenal and armaments factory. The first known purchase of a gun was in 1384, and the great bombard Mons Meg was delivered to Edinburgh in 1457. The first recorded mention of an armoury for the manufacture of guns occurs in 1474, and by 1498 the master gunner Robert Borthwick was casting bronze guns at Edinburgh. By 1511 Edinburgh was the principal foundry in Scotland, supplanting Stirling Castle, with Scottish and European smiths working under Borthwick, who by 1512 was appointed master melter of the kings guns. Their output included guns for the Scottish flagship, the Great Michael, and the Seven Sisters, a set of cannons captured by the English at 