The name Reilly is among the first twelve most frequently found surnames in Ireland. In Gaelic it s spelled O'Raghailligh, the descendant of Raghaalach. The word "raghallach" in Gaelic means impetuous. The name has many spellings in English such as Reilly, Riley and O'Reilly. The O'Reilly are of the same Celtic stock as the O'Rourkes and with them ruled Breffny, the O'Rourke's in the West and the O'Reilly's in the East.  Breffny is modern day county Caven. In addition the O'Reilly chieftains ruled parts of Counties Meath, Westmeath and Longford. The heads of the clan were elected chief over all Breffny. From the 13th to 16th centuries the O'Reillys maintained a forceful armed vigil to protect their lands from the English. During these years they became known as calvary men and fearless soldiers.  They maintained this independence to the days of Cromwell. An O'Reilly regiment of 800 infantry and 200 cavalry fought under Hugh O'Neill in the Elizabethan wars. Later they contributed to Owen O'Neill's victory at the Battle of Benburb. "Myles the Slasher" O'Reilly lives in tradition as a symbol of the dauntless but hopeless struggle against Cromwell.  The O'Reilly lands were taken after the Cromwellian War. Afterward many O'Reilly's made names for themselves in France, Austria and Spain. Five O'Reilly's were Archbishops of Armagh and Primates of Ireland and some have become famous authors and poets.