The life of Hilarion was written by Jerome in 390 at Bethlehem. Its object was to further the ascetic life to which he was devoted. It contains, amidst much that is legendary, some statements which attach it to genuine history, and is in any case a curious record of the state of the human mind in the 4th century. A theory started in Germany, that it was a sort of religious romance, seems destitute of foundation. It may possibly have been, in Jerome's intention, a contribution to the church history the writing of which he proposed but never executed. (See the Life of Malchus, c. 1.)
Source: The Life of S. Hilarion (New Advent)