Mob Quad is a four-sided group of buildings from the 13th and 14th centuries in Merton College, Oxford, surrounding a small lawn. It is often claimed to be the oldest quadrangle in Oxford and elsewhere, although Merton's own Front Quad was actually enclosed earlier (albeit with a less unified design) and Corpus Christi College, Cambridge, says that its own Old Court is the oldest structure of its type in either Oxford or Cambridge. The quadrangle pattern has since been copied at many other colleges and universities worldwide.
It was built in three distinct phases. The oldest part is the college's Treasury or Muniment Room that stands above and behind the arch in the north east corner. The roof of this part is strikingly steep and is made of stone in order to protect it (and its contents) from fire. The steep pitch of the roof is necessary to support the weight of the stone. The present roof was restored with new Purbeck stone in 1966. The upper floor has always been used to store the college muniments, while the ground floor was probably the original bursary. It is not known exactly when the building was completed, but there are references to it in the college accounts for 1288 and 1291. The Muniment Room being built above a vaulted arch is suggested as evidence that the range of buildings to the south was either planned at the time of the original design or was replacing an existing building.
