Above is the map of the fullest possible extent of the empire, including eventually abandoned German territories up to the Elbe river, the temporary Dacian, as well as the Armenian and Persian territories of emperor Trajan and the advance to the Antonine Wall in Scotland under emperor Antoninus. The boundaries drawn in black are an attempt at showing the current day national boundaries in relation to the empire.
Below you find a list of nations which were either definitely part of the Roman empire, or possibly so. Also included are some countries which had some frontline outposts in them.
The principal modern day nations of the Roman Empire are in bold print. Other countries which only saw some form of Roman occupation, or of whose effective membership of the empire I am unsure of, are listed in normal print.
| Albania | – |
| Algeria | – |
| Andorra | – |
| Armenia | With the annexation of the ancient kingdom of Armenia by emperor Trajan all of modern day Armenia will have become part of the empire. |
| Austria | – |
| Azerbaijan | With the annexation of the ancient kingdom of Armenia by emperor Trajan part, if not all, of modern day Azerbaijan will have become part of the empire. |
| Belgium | – |
| Bosnia-Herzegovina | – |
| Bulgaria | – |
| Croatia | – |
| Cyprus | – |
| Czech Republic | The initial conquest of German territories up to the river Elbe under emperor Augustus may well have included a small part of the Czech Republic. Also the campaigns of emperor Marcus Aurelius most likely conquered a considerable amount of Czech territory, though these gains were abandoned by his son Commodus without ever being recognised as a province. |
| Egypt | – |
| France | – |
| FYR Macedonia | – |
| Georgia | With the annexation of the ancient kingdom of Armenia by emperor Trajan part, if not all, of modern day Georgia may have become part of the empire. |
| Germany | – |
| Greece | – |
| Hungary | – |
| Iraq | – |
| Israel | – |
| Italy | – |
| Jordania | – |
| Kuwait | If any part of northern Kuwait was part of the short-lived province of Mesopotamia, created by emperor Trajan, I am unsure. Though it may well have done. |
| Lebanon | – |
| Liechtenstein | – |
| Luxembourg | – |
| Lybia | – |
| Malta | – |
| Monaco | – |
| Morocco | – |
| Netherlands | – |
| Palestine | Not an internationally recognized nation, It would have been part of the Roman province of Judaea. |
| Portugal | – |
| Romania | – |
| San Marino | – |
| Saudi Arabia | With emperor Trajan’s annexation of part of the kingdom of Nabatea as the Roman province of Arabia Petraea, a small part of the Red Sea coast of Saudia Arabia became part of the Roman empire. |
| Slovakia | Slovakia was home to several forward positions of the Roman frontier system. Also the campaigns of emperor Marcus Aurelius most likely conquered considerable parts of Slovakia, though they were abandoned by his son Commodus without ever being recognised as a province. |
| Slovenia | – |
| Spain | – |
| Sudan | To what extent the Roman province of Aegyptus extended into Sudan I am unsure of. Though it must have extended some way into this country to border on the kingdom of Nubia. |
| Switzerland | – |
| Syria | – |
| Tunisia | – |
| Turkey | – |
| United Kingdom | – |
| Vatican City | – |
| Yugoslavia | – |
Historian Franco Cavazzi dedicated hundreds of hours of his life to creating this website, roman-empire.net as a trove of educational material on this fascinating period of history. His work has been cited in a number of textbooks on the Roman Empire and mentioned on numerous publications such as the New York Times, PBS, The Guardian, and many more.