After Matthias' death in 1352, 23-year-old Peter Parler assumed control of the cathedral workshop as master builder. He was son of the architect of the Heilig-Kreuz-Münster in Schwäbisch Gmünd. Initially, Parler only worked on plans left by his predecessor, building the sacristy on the north side of the choir and the chapel on the south. Once he finished all that Matthias left unfinished, he continued according to his own ideas. Parler's bold and innovative design brought in a unique new synthesis of Gothic elements in architecture. This is best exemplified in the vaults he designed for the choir. The so-called Parler's vaults or net-vaults have double (not single, as in classic High Gothic groin vaults) diagonal ribs that span the width of the choir-bay. The crossing pairs of ribs create a net-like construction (hence the name), which considerably strengthens the vault. They also give a lively ornamentation to the ceiling, as the interlocking vaulted bays create a dynamic zigzag pattern the length of the cathedral.