Augustinian Friary

In the 13th century, the Nangle family, also known as deAngulo, seized the north-western region of what would become the barony of Costello following the arrival of the Anglo-Normans in the west. Around Lake Mannin, a Fitzgeralds branch is notable.

A 1932 newspaper snippet references 1249 as the year the Fitzgeralds established their presence, suggesting they built a manor and fortress on Friary Hill. This Ballyhaunis region eventually transitioned to the Nangles, later adopting the MacCostello name. Notably, the MacJordan Duff (or Dubh) subset of the MacCostello lineage centered around Lake Mannin and Ballyhaunis, establishing Rathnaguppaun as their primary fort. By 1282, the MacJordan Dubh took control of the Ballyhaunis vicinity, maintaining rule until 1586. This Costello line constructed the renowned Augustinian Abbey.

The Abbey entrance bears the date 1430, aligning with Rome's Augustinian records that cite a 1432 'recently founded' Irish Augustinian establishment. Supporting this, Friar Philip Nangle is tied to the foundation, marking Ballyhaunis as the sole Augustinian foundation linked to the Nangle family.