This text combines an account of the Ottoman siege of Constantinople led by Murad II in 1422 with praise of the Virgin Mary to whom the author attributes the city's salvation.

Kananos's account begins by describing how the Ottoman army devastated the area around the city. It then discusses how, under the command of Sultan Murad II and one of his generals, Michael Bey, the Ottomans began preparations for an assault on the walls and employed a variety of siege weapons. They were accompanied, he writes, by Mersaita, a Muslim holy man who predicted the city's fall. Kanonos writes that, greatly outnumbered and lacking effective leadership, the defenders initially despaired. He vividly describes a direct attack on the walls, how a large segment of the city's population – including women and monks – participated in the battle, and the defenders’ success against overwhelming odds. Kananos attributed the victory to divine assistance in the form of the Mother of God, whose appearance on the city walls caused the Turkish army to flee. Other historians offered more mundane explanations: according to Doukas, Murad abandoned his efforts after receiving news of an uprising by a rival in Asia Minor, while Chalkokondyles cites Murad's frustration with the assault's lack of progress.

The text combines historical narrative in the Byzantine tradition with a tribute to the Virgin Mary in hagiographical style. The author claims that the text is written in an accessible style of Greek and intended to reach a broad audience. The sources are largely unclear. The text includes allusions to classical authors and other accounts of sieges. An oration of Gregory of Nazianzus serves as a model for one section of the text.

John Kananos is only known from this text. The writing style indicates that the author was fairly well- educated, familiar with Byzantine historiography, and skilled in rhetoric. A Laskaris Kananos traveled extensively in northern Europe in the fifteenth century. We have no basis to say whether he was the author, or related to him.