The whole letter is well worth reading; here is just a short extract:
The case of Rome is worth studying. How a small town on a river became the center of one of the mightiest empires the world has known, eventually dominating thousands of other small towns on rivers, is a source of many lessons. That Rome was mighty is not to be doubted. The sheer size the empire achieved is breathtaking: from the Firth of Forth to the Euphrates, from the Tagus to the Rhine, spilling over into Northern Africa, for a time the Romans ruled over most of the world known to them. What they didn’t rule over wasn’t worth having, they felt: they left what was beyond their frontiers to “barbarians”.
Another measure of their greatness can be found in the Roman influences that continue to be felt to this day. Rome’s local lingo, Latin, became the mother language of most of Europe, and Italian, French, Spanish and Portuguese are still spoken all over the world. (The Germanic hordes beyond the Rhine, meanwhile, have managed to sponsor only one international language, albeit a successful one, English.) We also owe the Romans our calendar, with its twelve months and 365 1/4 day years; three days in our week hark back to three Roman days—Moonday, Saturnday and Sunday; and though we now use the Roman number system (i, ii, iii, iv, v, vi...) only occasionally, we use their 26-letter alphabet constantly.
Despite their power and might, another lesson about the Roman Empire forces itself upon us: how it’s all gone. The Romans reigned far and wide for centuries but now their empire has vanished entirely. A Roman today is simply someone who lives in Rome, a city that is beautiful because of its clutter of ruins. Such has been the fate of all empires: the Roman, the Ottoman, the British, the Soviet, to name only a few European empires. Which will be the next empire to fall, the next to rise?
[Thanks to rogueclassicum for bringing this to my attention]