He was the first writer on geometry, and the book he wrote bears his name. The following are some of his sayings: ‘The geometrical line is an abstract idea, rendered visible by a physical instrument.’ A man said to him: ‘I shall not rest till I take your life’; but he replied: ‘I shall not rest till I remove your anger.’—‘Do not foment enmity between two brothers, because a trifle will again reconcile them, and your reward will be repentance.’