The Romans used primarily thrusting attacks by short sword and pilums. This allowed them to stand practically shoulder-to-shoulder, whereas the Celts using the long sword and swings naturally needed considerably more room.
Somewhere in the dusty vaults of the old mind, I seem to remember that a Celt swinging a long sword needed a minimum of six feet on either side to avoid pinking his buddies in the attack.
When attacking a massed Roman formation, each Celt warrior (and the room necessary to use his weapon efficiently) wound up having to face Roman soldiers standing shoulder-to-shoulder, which probably winds up with each Celt dealing with three to five Roman soldiers at a time. Not the best of odds.
Strategically speaking, this meant that in head-to-head battles the Roman front line always outnumbered the Celt front line.
Just as important as far as strategy went, the Celts favoured the classic 'scream-and-leap' school of warfare, while the Romans took a more, shall we say, scientific approach, using discipline and fighting as a unit, rather than the individual style of the Celts.
As to your initial question: a typical Celtic sword on display at the Imperial War Museum has a blade about 31 inches +/- in length and one inch wide. Total sword length is in the neighborhood of 37 to 40 inches. Weight, if I remember correctly, is in the 2 pound range. While it has a point, it is primarily a chopping and slashing weapon, and was no doubt used in that fashion.
Roman swords, on the other paw, ran an overall length of about 28 inches +/-, with a blade of 19 inches lengthwise and 2 inches in width, weight ~ 2.5 pounds. The Roman
gladius, particularly the
Maintz pattern, had a pronounced point for thrusting, although the later styles were just as effective.
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LawDog