Conservators working in the Old Monastery of Taxiarches in Aigialeia West Greece, on the Peloponnese peninsula, have uncovered a mural portrait of the last Byzantine emperor, Constantine XI Palaiologos (r. 1449-1453). It is the last portrait of a reigning Byzantine emperor in a monumental painting known to survive and the only portrait of Constantine made during his very brief reign. The portrait was found under a later layer of murals in the monastery’s church. The painting depicts a bearded man wearing a diademed crown with a photostefano (halo disk) behind his head. He holds a cruciform scepter and wears a purple cloak embroidered with gold. The garment is decorated with medallions, most prominently a double-headed eagle, emblem of the Palaiologos dynasty emperors and senior members of the imperial family. The crown between the two heads identifies the subject as the emperor himself. It is not the idealized, allegorical portraiture typical of Byzantine art, but rather a realistic portrayal that conveys the individualized facial features of the man. This was not an official portrait created from an imperial-issue template, as was customary at the time; it was painted by someone who saw the emperor and painted what he saw. Constantine XI Palaiologos had a very short reign at the end of a tumultuous, war-torn period that culminated in the demise of the moribund Byzantine Empire. Before he ascended the throne, he was despot (initially a court title given to the son of the emperor that evolved into a ruler of an independent principate) of Morea for five years. We know from the Byzantine Greek historian Laonikos Chalkokondyles that Constantine’s brothers, Demetrius and Thomas, financed the renovation of the monastery when they were co-despots of Morea in 1449. The painter of the Taxiarches monastery portrait was probably from Mystras, the capital of Morea and a cultural center under the Palaiologoi, and was commissioned to paint the portrait by Demetrius and Thomas.