The remains of a church he founded at Disert Aengusa, near Ballingarry, in the county of Limerick, may still be seen.
The Monastery of Tamhlacht (Tallaght), near Dublin, was founded in the year 769, by St.Maelruain, on a site offered "to God, to Michael the Archangel, and to Maelruain," by Donnach, the pious and illustrious King of Leinster.

St.Aengus presented himself at this monastery as a poor man seeking for service, and was employed for some time in charge of the mill or kiln, the ruins of which have but lately yielded to "the improving hand of modern progress." Here he remained hidden for many years, until, by some happy accident, his humility and his learning were at once discovered.
Aengus composed his "Festology" in the reign of Hugh Oirdnidhe (the Legislator), who was Monarch of Ireland from the year 793 to the year 817.

Hugh commenced his reign by attaching the province of Leinster, and then marched to the confines of Meath.

The Archbishop of Armagh and all his clergy were commanded to attend this expedition, for such had hitherto been the custom.

The ecclesiastics, however, protested against the summons, and complained to the king of the injustice and inconsistency of demanding their presence on such occasions.