Peter Berresford Ellis (who writes popular mysteries under the name Peter Tremayne) has written quite a useful new history. "The Celts: A History" explains that by around the third century B.C., Celtic people had spread west to Ireland, east to Turkey, north to Belgium and south to Spain. They had also developed innovative agricultural techniques adopted by the Romans and cut the first roads through black European forests. Overall, Ellis successfully argues that the Celts - which is to say, the Irish, Manx, Scots, Welsh, Cornish, and Bretons - made contributions to Western culture which survive to this day. ($13 / 235 pages / Carroll & Graf)