Many of the early chronicles did not survive for a number of reasons. First, the earliest manuscripts prior to the 15th century were rare and extremely costly. (A 1273 Pagan manuscript of "Tripiṭaka" cost 3000 "kyats" of silver, which could buy over 2000 hectares of paddy fields.) The cost of producing manuscripts (creating as well as recopying) did come down in the Ava period as literacy rates improved, and the Burmese literature "grew more voluminous and diverse". Even then, most did not survive warfare, the main factor in destruction of historical records in Burmese history. Burmese history is littered with instances of conquering forces destroying the conquered's records: Pagan records in 1287 during the Mongol invasions; Ava records in 1525 and in 1527 by the armies of Confederation of Shan States; Hanthawaddy records in 1565 by a rebellion; Toungoo records in 1600 by Mrauk-U forces; more Toungoo records in 1754 by Restored Hanthawaddy; remaining Hanthawaddy records in 1757 by Konbaung forces; Arakanese records in 1785 by Konbaung; Konbaung records in 1885 by the British. Perhaps not surprisingly, the most complete surviving chronicles are those of Upper Burma-based dynasties, which often were the victors of the wars. Even for those that survived the wars, "there were no record-room methods; mildew, ants, the accident of fire prevented many manuscripts reaching a great age". Those that survived did so only because private individuals outside the capital had painstakingly copied the original palm leaf manuscripts. The survival of the manuscripts was also facilitated by the increasing literacy rates in the Irrawaddy valley. In the 15th century, when the literacy rate was still low, the scribal work was chiefly handled by monks, but by the late 18th century, it was routinely handled by commoners as adult male literacy exceeded 50 percent.