Moygara Castle, with its four towers, gatehouse, and high curtain walls, is one of the most impressive masonry-built monuments in north Connacht. Constructed in the late fourteenth/early fifteenth century by the O'Garas, the castle functioned as a centre of their lordship of Coolavin. This study of Moygara Castle marshals various fields of expertise— history, archaeology, architecture, geography, genealogy, geophysical survey and DNA analysis— to provide much-needed information about life in later-medieval Gaelic Ireland.