Leadership of the Pachomian Federation
Before the death of Pachomius the Great, Horsiesios served as superior of the monastery of Sheneset (Chenoboskion). When Pachomius died, he had named Petronios as his successor at the head of the Koinonia rather than the more prominent Theodore; Petronios himself died later the same year, and Horsiesios was then placed in charge of the whole federation. His first tenure as superior is generally dated to the years 346 to 350.
This first period of leadership was marked by serious difficulty. Many of the elder monks across the Pachomian houses regarded Horsiesios as too weak to govern, refused to work or obey, and the federation began to fall apart, with monks demanding new leadership. Theodore the Sanctified, who had withdrawn to a distant monastery, returned to placate the rebellious monks and effectively assumed the governance of the communities for some eighteen years, while insisting that he acted only on behalf of Horsiesios. Horsiesios resigned the active superiorship around 350.
Second Tenure and Return to Authority
After Theodore the Sanctified foretold his own death, which came to pass in 368, Horsiesios once again took his place as head of the Pachomian communities, this time in both title and authority. According to the Western tradition, his return to office followed counsel from Saint Athanasius the Great of Alexandria. His second tenure is dated from 368 until his repose around 387.
The standing of Horsiesios within the Church of his day is reflected in the surviving correspondence of Saint Athanasius of Alexandria, whose letters praise Theodore while acknowledging Horsiesios's position and address him as abbot and father of monks.
Writings
Horsiesios is remembered as an author as well as an administrator. His principal work is the Testament of Horsiesios, an extended instruction on the monastic life; the account of his writings notes that it sets out teaching for the whole of monastic discipline, drawing on nearly the whole of the Old and New Testaments. In 404 Saint Jerome translated this work into Latin under the title Liber Horsiesii (also known in Western tradition as the Doctrina de institutione monachorum).
Beyond the Testament, seven catecheses and four letters are attributed to Horsiesios in Coptic. Tradition also associates Horsiesios, together with Theodore, with assisting Pachomius in the composition of the Pachomian monastic rule.
