David the Dendrite (died 540), also known as David the tree-dweller and David of Thessalonika, is a patron saint of Thessaloniki and a renowned holy fool. Originally from Mesopotamia, David became a monk at the Monastery of Saints Merkourios and Theodore outside Thessaloniki. Famed for his sound advise, crowds would hound him for words of wisdom and prayer. Wishing a quiet, contemplative life, David fled to the seclusion of an almond tree, where he lived for three years. He left the tree to petition the Byzantine emperor Justinian in Constantinople to send soldiers to defend Thessaloniki from attack. David died in 540 as his ship was in route to Macedonia.