Connacht contains what are now the counties of Mayo, Sligo, Leitrim, Roscommon, and Galway. The ancient capital was Crúachu, today called Rathcroghan in Roscommon. Connacht roughly coincides with the area known as Nagatae in Ptolemy's 2nd century geography. The name Connacht is from Conn Cetchathach or Conn of the Hundred Battles, an early first century Irish king. In mythic narrative, the Fir Bolg tribes of Milesian descent ruled most of Connacht until the beginning of the 4th century, when that tribe was defeated at the First Battle of Mag Tuired.




In the Irish epic Tain Bo Cuailnge (Cattle Raid of Cooley), the ruler of Connach is Queen Mebd whose royal residence was at Crúachu. In this story, Medb and Connacht are symbolically intertwined, as one is often synonymous with the other. Other legendary figures connected with Connacht are King Ailill and Findabair, daughter of Ailill and Medb, Crimthann Cass, Eogan, Guaire and Lairgnean. Cathal Mor of the Wine-Red Hand is also a personification of Connacht. Niall Noigiallach (Niall of the Nine Hostages) also has his roots in this region. He was the son of Eochaid Mugmedón (King of Connacht) and a captured British slave named Cairenn. The tale of his ascension to the high kingship of Eire is told in Echtra Mac nEchach Muigmedóin.





In ancient times, the capital of Connacht was Crúachu, located in what is now Rathcrogan between Belanagare and Elphin in County Roscommon. The magnificent fortress of Medb and Ailill is immortalized in many early Irish narratives, including the Tain Bo Cuailnge. It is the counterpart of Tara in Meath, Emain Macha in Ulster, and Dun Ailinne in Leinster. This royal site was symbolic of Connacht's power and wealth. It is described in legend as both luxurious and huge, with seven compartments for residents.

Archaeological findings suggest that this site as built by Goidelic invaders who set it up as their capital in order to rule over the native people. The area encompasses about two square miles, including 5 concentric circles, several mounds that may be passage graves, and a large number of earthworks. A seven foot tall standing stone is said to mark the resting place of King Dathi, the last pagan king of Ireland. There are extensive ogham inscriptions at many places around the area.


Located on the shores of Lough Mask, some 25 miles northwest of present-day Galway, Crannog Niall is a pseudo-historical Role Play site for the earliest of the western Ui Niall.