King Vladislav II had a tower built here in 1496 as a cannon bastion overlooking the stag moat. The original was destroyed in a fire, but this tower was rebuilt as a home and workshop of the bellfounder Tomas Jaros, who in 1549 made the bell for St Vitus Cathedral's tower. Later it became a laboratory for alchemists. The famous Edward Kelley and others worked here on experiments that convinced Emperor Rudolph II that they could transmute lead into gold.