The use of uranium in its natural oxide form dates back to the year 79 CE. It was used in the Roman Empire to make ceramic glazes yellow. Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy. It was found by R. T. Gunther of the University of Oxford in 1912. In the late Middle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic). In the early 19th century, the world's only known sources of uranium ore were these mines.