Mod Offical Support and Home Page:
http://forums.taleworlds.com/index.php/board,261.0.html

IMPERIUM ROMANUM 1.9.4 (BRYTENWALDA SUB-MOD)
You do NOT need BRYTENWALDA to play this mod just the installer!
If you enjoy the mod endorse it!
Features :
- Realistic combat ( as far as brytenwalda/warband engine will allow ) , deadly weapons no "superhero" charges
- Challenging campaign game-play
- Realistic Roman flags
- The only true representation of Roman battle order in any mod so far
- A truly complete Roman troop tree
- Unparalleled variety of realistic Roman units 10 Auxiliary Cohorts , 7 Legions, 4 Cavalry Cohorts all proven to be present in Britain 43 AD
- Reworked British factions totally
- New Authentic equipment for Romans/Britons made by Vympel + friends
- Realists Roman forts by Adorno
- Realistic ranking system for Roman legionaries and auxiliary
- Completely different musical environment fitting the setting and glorious ferocity of Roman warfare
- Only period specific equipment availability
- Defence pact between Roman factions from th estart (Motomataru)
- Different pricing system
- Optional Polished Landscapes graphical addon
- Modular options format to provide flexibility to the ways of the playing the mod , first mod in MB to have this options

History:
"By the 40s AD, the political situation within Britain was apparently in ferment. The Catuvellauni had displaced the Trinovantes as the most powerful kingdom in south-eastern Britain, taking over the former Trinovantian capital of Camulodunum (Colchester), and were pressing their neighbours the Atrebates, ruled by the descendants of Julius Caesar's former ally Commius.

Caligula planned a campaign against the British in 40, but its execution was bizarre: according to Suetonius, he drew up his troops in battle formation facing the English Channel and ordered them to attack the standing water. Afterwards, he had the troops gather sea shells, referring to them as "plunder from the ocean, due to the Capitol and the Palace". Modern historians are unsure if that was meant to be an ironic punishment for the soldiers' mutiny or due to Caligula's derangement. Certainly this invasion attempt readied the troops and facilities that would make Claudius' invasion possible 3 years later (e.g. a lighthouse was built by Caligula at Boulogne-sur-Mer, the model for the one built soon after 43 at ancient Dover).

Three years later, in 43, possibly by re-collecting Caligula's troops, Claudius mounted an invasion force to re-instate Verica, an exiled king of the Atrebates. Aulus Plautius, a distinguished senator, was given overall charge of four legions, totalling about 20,000 men, plus about the same number of auxiliaries. The legions were:
Legio II Augusta
Legio IX Hispana
Legio XIV Gemina
Legio XX Valeria Victrix
The II Augusta is known to have been commanded by the future emperor Vespasian. Three other men of appropriate rank to command legions are known from the sources to have been involved in the invasion. Gnaeus Hosidius Geta, who probably led the IX Hispana, and Vespasian's brother Titus Flavius Sabinus II are mentioned by Dio Cassius (Dio says that Sabinus was Vespasian's lieutenant, but as Sabinus was the older brother and preceded Vespasian into public life, he could hardly have been a military tribune). Gnaeus Sentius Saturninus is mentioned by Eutropius, although as a former consul he may have been too senior, and perhaps accompanied Claudius later."
http://en.wikipedia.org/wiki/Roman_conquest_of_Britain#Claudian_preparations