Citadel of Trebizond
The Citadel of Trebizond has eight phases of construction, mostly dating to the 13th and 14th century. Parts of the palace have also survived.
The Byzantine Monuments and Topography of the Pontos by Anthony Bryer & David Winfield
Byzantine Painting at Trebizond by Millet and Talbot Rice
Byzantium’s Other Empire: Trebizond by Antony Eastmond
Byzantine Architecture by Cyril Mango
Oxford Dictionary of Byzantium edited by Alexander Kazhdan