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 king's 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 Flodden in 1513. Sir Thomas Howard, England's Lord Admiral, admired their graceful shape and brilliant finish, declaring them the most beautiful [cannon] for their size and length that he had ever seen. From 1510 Dutch craftsmen were also producing hand culverins, an early firearm. After Flodden, Borthwick continued his work, producing an unknown number of guns, of which none survive. He was succeeded by French smiths, who began manufacturing hagbuts (another type of firearm) in the 1550s, and by 1541 the castle had a stock of 413.