The original SoulCalibur takes place in 1587, and the ones after that, well, they never exactly say, but within a few years of that date. But like Moogi says, they play pretty fast-and-loose with real history, so, yeah. And as for justifying him - well, more the fact he goes from "pirate who vows to kill everyone and never fight for Spain" to "Spanish national hero." Y'know? As for Arthur... hmm. I think one of the latter two would be best - Tiberius leading a new Roman Empire would be a simple solution, but the other one fits better into the timeline. cfkane's decision, I think.