Contrary to popular belief, Magna Carta was sealed, not signed. King John, like other medieval kings, authenticated his charters by having the Great Seal of England attached to the lower edge of the parchment. A seal press was used to create the impression on the two-sided Great Seal and to attach it to the charter. It applied pressure to two metal matrices engraved with the design on the seal, two discs of beeswax and the plaited silk cords which joined the seal to the document. A similar press, shown here, was made for Canterbury Cathedral around 1232. This press, which has an iron handle and a copper alloy mechanism, is mounted on an oak block. The seal was the most vulnerable part of any medieval charter and, of the four surviving 1215 Magna Carta documents, only one — now in the British Library — retains any trace of its original seal.