He later retired to a monastery to write what was intended to be his great work, a chronicle of world history, Ekloge chronographias (Ἐκλογὴ Χρονογραφίας), or Extract of Chronography.
According to Anastasius Bibliothecarius, George "struggled valiantly against heresy [i.e. Iconoclasm] and received many punishments from the rulers who raged against the rites of the Church", although the accuracy of the claim is suspect.
Following on from the Syriac chroniclers of his homeland, who were writing in his lifetime under Arab rule in much the same fashion, as well as the Alexandrians Annianus and Panodorus (monks who wrote near the beginning of the 5th century), George used the chronological synchronic structures of Sextus Julius Africanus and Eusebius of Caesarea, arranging his events strictly in order of time, and naming them in the year which they happened.
But in spite of its religious bias and dry and uninteresting character, the fragments of ancient writers and apocryphal books preserved in it make it especially valuable.
Anastasius, the Papal Librarian, composed a Historia tripartita in Latin, from the chronicles of George Syncellus, Theophanes Confessor, and Patriarch Nicephorus.