These stones abound with folklore involving Brian Boru and a quarrel that resulted in the death of the King of the Leinster (who is thought to be buried about 1/2 mile away at the Knockaunrilaghin or Capstone of the King of Leinster). The Graves or stones themselves are thought to be where the Leinster warriors fell.
There are a number of theories as to what they actually are and most agree that they are far older than the time of Brian Boru and are likely to date back to prehistoric times. Some have suggested that they are the remains of a Court-Tomb, Wedge Tomb or even a stone circle.
The local Arra Historical & Archaeological Society are currently working with the Adopt a Monument Scheme to try and answer this question as to what they actually were. For more on the stones and surrounding area see here: