How did the Romans sharpen their swords?

Casually, to maintain an existing weapon, they would use a whetstone and carefully rub it against the blade's edges, at a certain angle and with a certain manner of stroke. To give a blade its initial edge, typically it would be sharpened with a grinding wheel by the cutler who assembled and shaped it. Presumably, if you wanted a more professional sharpening of your dulled sWord, or you wanted to file down a chip in the blade, you could take it to a cutler and have it resharpened by a grinding wheel, though doing this too often would probably result in a thinner blade.