The following is intended to accomplish two things: show the history of Britannia as it developed in the real world, and illustrate and illuminate the rules of the game.
This is the historical arrangement, as best we can reconstruct it and shoehorn it into the game. These are not the optimal moves for play of the game, in large part because gamers have historical foresight, and know, for example, that the Belgae will be their antagonists in Turn 1 despite having submitted.
Roman Nation Turn 1, first half of Major Invasion.
The map shows the following positions before combat:
The Romans can move three areas, not two. They start in the Channel, so can move as far as South Mercia and Suffolk, provided there are overruns in the intervening areas. This requires two Romans in Sussex and Essex to outnumber the Belgae 2-1. To reach Downlands the Romans must have an overrun in Essex or Wessex, as well. The Romans must stop in Downlands, because it is difficult terrain. The Romans could have moved from Wessex to Avalon to Hwicce, if they had wished. But in the actual event, the Romans concentrated on the more civilized (more Romanized) southeast first.
In all the combats other than Downlands, each Roman army needs to roll a 4, 5, or 6 to kill a Belgae, and the Belgae need to roll a 6 to kill a Roman. In Downlands, owing to difficult terrain, the Romans kill the Belgae only on a roll of 6 (and that’s why there are three Romans there instead of two).
The Romans specify an order of combat that leaves Suffolk to last. At that point the Belgae have been reduced to four areas and choose to submit before the fight in Suffolk. We’ll say that the six Belgae in the other combats are eliminated, and one Roman. Notice that the Belgae in South Mercia could survive one throw of the dice and then retreat to North Mercia. The others have nowhere to retreat to.
The Romans build forts in all the territories taken, but NOT in the Belgae-occupied areas. (The Romans did not actually build forts everywhere; the forts represent Roman administrative control as much as anything.)
The Romans in Suffolk withdraw to Wessex and Downlands via the Roman Roads.
The British did not put up a great resistance, because many wanted the advantages of Roman civilization. Moreover, we portray the Belgae as a single nation, but in fact there were several competing nations in the Belgae area, and a Roman pretext for invasion was to help one of their clients against another British tribe in southeast England.
The Romans score six points for forcing the Belgae to submit. The Belgae score two points for killing a Roman army (they get six for an army on their nation turn only).
Roman Nation Turn 1, second half of Major Invasion.
The map shows the following positions before combat:
The Romans then moved to take Wales, in part because Caratacus, a leader of British resistance, had taken refuge in Wales. Their main thrust was to the northeast when Caratacus fled there.
At this point the Romans have Roads to help them, but they cannot get past the difficult terrain to the clear terrain areas of Wales. They must use an overrun in March in order to get to Clywd.
The Romans fight in order from south to north, assuming that the Welsh will submit when they are reduced to five areas (Cornwall, Dyfed, Gwynedd, Clywd, and Powys). However, the Welsh resisted mightily, and do not submit. (This would probably not be wise in the game, but reflects the difficulty the Romans had in Wales.) The Welsh are reduced to three territories. The Romans build forts in the newly-conquered territories. If the Welsh had submitted at five, then the Romans in Clywd and Powys would have redeployed via Roads to other areas.
We’ll suppose that the Welsh army in Clywd survives and retreats to Gwynedd, and the army in Devon survives and retreats to Cornwall. The others, and one Roman, are eliminated. The Brigante in March is eliminated. Notice that the Romans left one army in South Mercia.
The Welsh score two points for killing a Roman army.
It is now the Belgae nation turn, and they rebel. They have three clear terrain and one difficult, for a total of seven Increase points. They get one army and place their marker on the "1" on the Population Track. They also get an army and the leader Boudicca. They place all of these new pieces in Suffolk and attack as shown in the map below, three armies and Boudicca in South Mercia, two in Essex, and one in Kent. They can reach Kent thanks to the overrun in Essex. The armies in Lindsey and Norfolk cannot get to Kent, but they can be part of the overrun that enables an army from Suffolk to reach Kent.
In play of Britannia, the Romans are usually careful to leave armies in all three of these areas to protect the forts, and the Belgae may attack only one or two areas, rather than three. Sometimes the Belgae leave one (or even two) armies in Lindsey, both so that they won’t be overpopulated after attacking one area only, and also because they hope to survive there until Round V scoring.
In Essex the Belgae roll a 3 and a 5, sufficient to eliminate the Roman fort. The Roman fort rolls a 4, which misses (an army would have hit). In Kent, where there is equal strength, the Belgae are lucky and kill the fort without losing the attacking army.
In South Mercia the battle is more complex. The Belgae roll 2, 3, and 4, which are increased by the leader to 3, 4, 5. Because they need to kill the Roman army, and did not get a 6, neither Roman is harmed! The Romans, however, roll a 2 for the army and a 4 for the fort, both misses (the dice must be rolled separately because different "to hit" rolls are needed). The Romans choose not to retreat, and the Belgae choose to stay.
In the next round the Belgae roll 1, 4, and 5. The leader increases this to 2, 5, and 6. The 6 kills the Roman army, and the 5 kills the fort (because the army has also been killed). The Roman army rolls a 4, and the fort a 5, which results in two dead Belgae.
The Belgae have killed three Roman forts (which are turned over to show the destroyed fort side) and one army in their nation turn 1, sufficient for 24 points!
Other nations, Round 1.
The map below shows the positions after the other nations have played:
The Welsh have five Increase points, not sufficient for another army. A rather wild move would be to attack Powys with three armies, but the Welsh stand in defense where they are.
The Brigantes have 14 Increase points (IP), getting two armies and placing their marker on the two box on the Population Track.
The Caledonians place their marker on the three box, and do not move.
The Picts have seven IP, taking a new army and placing their marker on the one box.
None of these nations attack. In a normal Britannia game the Brigantes might be more active, or might not. The Picts might choose to attack Caithness (assuming the Caledonians haven’t abandoned it).
Round II. Roman Turn.
The Romans do not use Increase points. They have thirteen armies, so do not receive any reinforcements.
The Romans attack the Belgae, and try to force the Welsh to submit. Most of the Romans attack the Belgae; one moves through North Mercia to Suffolk to Essex, and another through North Mercia to South Mercia, so that the Belgae have nowhere to retreat to. The Romans will be able to build forts in those two areas even though they did not stop there.
In the battles all the Belgae are wiped out, and two Romans. The Belgae score four points for the Roman armies. The Romans get six points for killing Boudicca. They cannot build forts in the three areas where Roman forts were destroyed (the "destroyed fort" markers are not shown on the map, but would be there in the game). They do build forts in North Mercia, Suffolk, and Lindsey.
The Welsh submit, and the three Romans in Wales, using the Roads provided by forts, withdraw to March, North Mercia, and Lindsey.
At this point the Romans must be reduced to 12 armies owing to withdrawal of a legion. They have only 11, so there is no change.
Rest of Round II.
It is now the Belgae turn, but they no longer exist.
The Welsh, submitted, ask the Romans if they can get full rather than half Increase. The Romans say Yes. Five IP added to the five saved gives the Welsh another army, which they put in Dyfed, and their Population Track marker goes to four. [They are going to have overpopulation problems when they get another army, as right now they have three areas and the maximum six armies. At least they’re in good shape vs. the Irish next Round.]
Historically, the Brigantes remained neutral with respect to the Romans for some time, but finally conflict occurred, resulting in part from internal competition between Roman allies and enemies. Brigantes have 14 IP again, plus two saved, for 16. They get two more armies, and save four. The Brigs set up to give the Romans maximum trouble.[Note: In the game, the Brigantes cannot have more than 11 armies. Their marker would be put on the "5" on the Population Track. The map shows them with 12 armies.]
The Caledonians get an army, which they put in Caithness.
The Picts expect the Romans to be coming, and decide to mass against them:
Roman Nation Turn III.
With 11 armies, the Romans receive no reinforcements.
The Romans put four armies into York, overrunning it. Two more go to Bernicia (overrun), and then two to Lothian. Three attack Cheshire. (The Roman roads make this possible–all these armies move off the roads into York. One army moves from Lindsey to Norfolk, then via a second move to the roads in Suffolk, then along the roads and as its third move to York, thus securing Norfolk for Rome.) The Romans don’t have the resources to force the Brigantes to submit this time (that’s why the Brigantes put up the "shield wall" in York and Cheshire). They will likely be in a good position if the Brigantes intend to counterattack.
In the game, the Romans will try to force Brigante submission in Round 3 so that their Round 3 capture score will be higher (they score for areas held by submitted nations).
In reality, the Romans reached Pictland in the early 80s AD. The game timeline does not perfectly reflect reality; and if it did, there would be a couple very static, downright boring, Rounds, so it’s just as well . . .
I hope this walk-through has helped you understand the rules of the game.