In Byzantine literature, three different cultural elements are recognised: the Greek, the Christian, and the Oriental. Byzantine literature is often classified in five groups: historians and annalists, encyclopaedists (Patriarch Photios, Michael Psellus, and Michael Choniates are regarded as the greatest encyclopaedists of Byzantium) and essayists, and writers of secular poetry. The only genuine heroic epic of the Byzantines is the Digenis Acritas.