What does excalibur officially look like?
The correct time period for Arthur is the Dark Ages, sometime in the two hundred years after the removal of Romes’ Legions from Brittania. Arthur himself, if he existed, would have used the best arms and armour available, and that was still Roman lorica, and the two signature swords of the Empire: the gladius and spatha. Since Excalibur is always described as a sword that Arthur could use from horseback, it would have been a spatha, and was probably made of Damascus pattern welded iron to provide a springy core, with a tack-welded steel edge for strength and sharpness. Such a weapon would have been vastly superior to anything the northern tribes had, and would have cleaved through the native hide armors like a hot knife thru butter.