The map here is outdated. I would love to look into making a new one, but I recommend waiting for Holy Fury with the new map.
This map shows the maximum historical borders after Trajan's conquests. Unfortunately, this is not the map you need for the SPQR achievement (I really wish it were). You can find the requirements in roman_events.txt. A lot of it is defined by regions:
completely_controls_region = world_middle_east_jerusalem completely_controls_region = world_europe_south completely_controls_region = world_europe_west_iberia completely_controls_region = world_africa_north
In addition it lists France, England, Wales, Syria, and Anatolia + Armenia by duchies. Notice that you don't need the German lands up the the Germanic Limes. And you don't need Dacia. Or Babylonia (modern day Iraq). And North Africa includes those desert corridors towards Mali, and the Canary Islands, although those were never Roman