Monastic Life on Mount Athos
On Mount Athos, Theonas first lived as an ascetic at the Monastery of Pantokratoros, where he was ordained a priest. He afterward joined the brotherhood of Saint James of Kastoria at the Skete of the Honorable Forerunner above the Monastery of Iveron.
By tradition, on Bright Friday in the year 1518 Saint James and his brotherhood departed from Mount Athos, passing through the region of Thessalonica and settling for about a year at the Monastery of the Honorable Forerunner in Dervekista, in Aitolia. After James was martyred on November 1, 1519, leadership of the brotherhood passed to Theonas, who led the community back to the Monastery of Simonopetra on Mount Athos around 1520.