Plays about miracles wrought by holy men or saints or the sufferings and fortitude of martyrs were performed, usually at the great church festivals. Most nobles could read, though writing was still a specialized craft. There were books on animals, plants, and stones. The lives of the saints as told in the book "The Golden Legend" were popular. The story of the early King Arthur was told in the book "The History of the Kings of England". The story at this time stressed Arthur as a hero and went as follows: Arthur became king at age 15. He had an inborn goodness and generosity as well as courage. He and his knights won battles against foreign settlers and neighboring clans. Once, he and his men surrounded a camp of foreigners until they gave up their gold and silver rather than starve. Arthur married Guenevere and established a court and retinue. Leaving Britain in the charge of his nephew Modred, he fought battles on the continent for land to give to his noblemen who did him service in his household and fought with him. When Arthur returned to Britain, he made battle with his nephew Modred who had crowned himself King. Arthur's knight Gawain, the son of his sister, and the enemy Modred were killed and Arthur was severely wounded. Arthur told his kinsman Constantine to rule Britain as king in his place. The intellectual world included art, secular literature, law, and medicine. There were about 90 physicians. The center of government was a collection of tenants-in-chief, whose feudal duty included attendance when summoned, and certain selected household servants of the King. The Exchequer became a separate body. The payments in kind, such as grain or manual services, from the royal demesnes had been turned into money payments. The great barons made their payments directly to the Exchequer. The income from royal estates was received by the Exchequer and then commingled with the other funds. Each payment was indicated by notches on a stick, which was then split so that the payer and the receiver each had a half showing the notches. The Exchequer was the great school for training statesmen, justices, and bishops. The Chancellor managed the domestic matters of the Crown's castles and lands. The great offices of state were sold for thousands of pounds, which caused their holders to be on their best behavior for fear of losing their money by being discharged from office. One chancellor paid Henry about 3000 pounds for the office. Henry brought sheriffs under his strict control, free from influence by the barons. He maintained order with a strong hand, but was no more severe than his security demanded.