Actually, the Romans technically held out until the Fall of Constantinople, which was a lot further along than 700 years.
Also, considering the world and its mores at that time, the Romans were rather polite indeed. Usually a conquered people would see all the teen/adult males killed, the women dragged off to slavery (if not killed along with everyone else), and everything of value plundered. See also a huge chunk of Exodus and the conquest of Canaan (the Hebrews weren't exactly choir boys when it was they who had the strength and power, no?)
But, no - the Romans (usually) settled for taking a percent as slaves and then proceeding to absorb their culture, religion, and the better parts of what was left. Then they built roads, utilities, entertainment, and a whole shitload of things that were pretty effing amazing - for the time. Yup - they were brutal as fuck at times (see also Caesar's conquest of Gaul), but if the conquered people submitted, it usually went way the hell easier on them than it would at the hands of any other civilization at the time (save for the Greeks, but then the Romans pretty much absorbed most Greek philosophy, mathematics, religion, laws, etc etc...)