The ancient Greeks called them Keltoi and Galatai (Galatians; yes, as in the New Testament). Romans added Galli to the list. And probably added a bunch of unprintable epithets as well, since the Greeks/Romans and the Celts often fought. As noted above, it is difficult to tell whether we're dealing with a unified ethnic group or with diverse peoples who adopted the same equipment and economies. Julius Caesar wrote some interesting things about the Celts, some of which can be supported by the archaeological evidence. Good things to read about the early Celts include books by Vincent and Ruth Megaw, Barry Cunliffe, T.G.E. Powell, Stuart Piggott, Peter Wells and a host of others. Also the Asterix comics. Lots of loony stuff published about and attributed to them as well.

And since we're on the 'Cat, here's a musical question about the Celts: Once, when I was giving a lecture about the Celts in central Turkey (where three tribes migrated during the 3rd century BC), someone in the audience asked about bagpipes in Turkey, based on their conviction that the pipes were a traditional/standard Celtic instrument and that if the Celts were in the area around Ankara, then bagpipes should be there too. I didn't and still don't know of any archaeological evidence for bagpipes in the Celtic parts of Turkey, but do any M'catters know of any evidence for the pipes, either ancient or modern, in that area?