The Roman Empire spanned the Mediterranean and was a massive empire. Its borders were typically Hadrian's Wall in Britain, the Rhine and Danube rivers in Europe, the Parthian Empire in the east, and to the Sahara to the south.

The Roman Empire did expand outside of these borders and sometimes reached very far - sometimes in occupation and in other times as part of military campaigns. As these were frontier regions that were often very undeveloped or just occupied very briefly, so there are not normally many impressive Roman ruins to be seen today.

The Red Sea: The Farasan Islands
The Farasan Islands are a small group of coral islands in the Red Sea and today part of Saudi Arabia. They are located very far down the Red Sea just off the coast of Saudi Arabia, close to Yemen and Eritrea.

In the 1st century AD, these little islands were known as Portus Ferreseanus and they are believed to have housed the farthest Roman outpost from Rome. A Latin inscription found on the islands dating from 144 AD shows that the Romans built a garrison here. Administratively, the island was probably part of the Roman province of Arabia Felix before being transferred to the province Aegyptus (Egypt). They are nearly 4,000 from Rome.

Today these islands have become popular tourist destinations and there is a free ferry ride twice a day to the island from Jizan Port in Saudi Arabia.

Britain: Scotland And The Scottish Highlands
At a few times in its history, all of southern Scotland was part of the Roman Empire with campaigns going much further north.

The Romans didn't just build Hadrian's Wall across Britain - they built the Antonine Wall (twice) deep in Scotland.

The Romans built a series of supply forts, roads, and fortlets constructed on the routes up to the new frontier line of the Forth – Clyde isthmus in Scotland. They even campaigned as far north as Moray Firth in the Highlands (the Highlands of Scotland are very much worth visiting) and a Roman fleet even reached the extreme northern Orkney Islands off the northern Scottish coast.

But a couple of times they abandoned this northern frontier in favor of Hadrian's Wall in England. Scotland was likely a combination of being too unruly, too far, and not valuable enough for the Romans to really bother with.

Without a doubt, the Antonine Wall is the most important and substantial Roman ruin in Scotland today (but still there isn't all that much to see).

The Caucasus: Armenia
The ancient kingdom of Greater Armenia was at different times a client state or buffer state. It was mixed with the age-old rivalry between the Romans and the powerful Parthians (centered on the Iranian plateau).

Today Armenia has a very impressive Roman temple to visit - the Temple of Garni that was probably dedicated to the sun god Mihr. But this temple was more gifted to the Armenians with Roman architects etc. dispatched to build it.

Between 114 and 117 AD, the Parthian Empire finally collapsed and in this brief period, it seems that parts of what is today Armenia were incorporated into the Roman Empire.

Recently, (in 2018) archeologists discovered the easternmost Roman aqueduct. The aqueduct is unfinished and probably dates from the second century when the Romans briefly conquered Armenia and had control of the city of Artaxata (the old Armenian capital).

The aqueduct is located near Khor Virap close to the border with Turkey. After the region fell outside Roman control construction ceased and it was abandoned.

Iraq Down To Kuwait & Iran
While for most of history, the Roman border to the east ran roughly where the border between Iraq and Turkey today when the Parthians collapsed that all changed. The Roman province of Mesopotamia was a short-lived province created by Emperor Trajan in 116-117.

In Trajan's campaign, he conquered Armenia and rolled up the Parthian Empire. He managed to march all the way and capture the great Persian city of Susa deposing the Parthian King Osroes I. They sailed down the river all the way to the Persian Gulf.

But after his death in 117, the new Emperor, Hadrian (ruled 117 to 138) decided to relinquish these conquests east of the Euphrates River. They were just too far to be feasible or defensible. Never again would the Romans reach the Persian Gulf.

Additionally, the Romans expanded deep into Germany and parts of southern, Ukraine, Russia, Georgia, and more. But those are stories for another day.