The cathedral was built in the northern section of the courtyard and is dedicated to the Metamorphoseos tou Sotiros ('The Transfiguration of the Saviour'). As is well known, this feast is connected directly to the teaching about the appearance of miraculous light reported by St Gregory of Palamas and the other cloistered clerics during the 14th century, a few decades prior to the founding of the Monastery. It is not coincidental, therefore, that a number of Catholic monasteries which were founded during that period were also dedicated to the Transfiguration. Architecturally, the church follows the plan of the triangular, cruciform plan characteristic of the Athonite churches, with one basic difference: The elongation of the eastern vault and the addition of two polygonal structures (typikaria) to the two corners of the sanctuary make the shape of the cathedral unique.
On the basis of various first-hand accounts as well as recent archaeological research, the lead-roofed cathedral acquired the form it has today after three construction phases. The first dates to the period of the founding of the Monastery, and included the central nave, the eastern section of the entrance nave, and the chapel of the Κοιμήσεως της Θεοτόκου ('The Dormition of the Virgin Mary').
