The remaining ruins of 16th Century Legan Castle are listed as a Monument of Ireland, at the foot of the ruins sits an Ogham Stone, which is also listed as a Monument and dates back to 400-550 AD. Legan Castle belonged to the monks of Jerpoint Abbey, and later became residence of Sir Oliver Grace and the Grace family. In March 1650 Thomastown was under siege by Cromwell and Legan Castle took at hit.