The basic formation I use as Britannia is first to put my slingers up in front of my army. The enemy will do one of two things sit there and do nothing or charge. If they sit there, you move your slingers into range and pelt them. If they charge you'll get off a few volleys and the slingers will retreat, move them off to the side of your army, careful that your armys not in the way and continue pelting the enemy during hand to hand.

The next part of my basic strategy is to put all the warband in the army in a line in guard mode. Immediately behind this line are all my swordsman and woad warriors. I came up with this tactic early on because woad warriors have such terrible armor they simply cant be allowed to be attacked, however it works great with swordsman too.

Basically this setup has several advantages, if the enemy tries to overload one side of your line more than the other your heavy units that can change the tide arent locked into the front line and can be sent to attack the side where the main thrust is coming. The shock of a fresh heavy unit charging straight at the enemy after combat already been going on with the warband seems to break them every time. Keeping the swordsmen back guarantees you get the full charge bonus as the enemy is at a stop fighting the warband. Also the warband in guard mode since its so thick never seems to let a cavalry unit through it, which enhances the speed at which you kill the cavalry, especially when your unit of swordsman behind the warband comes charging through the warband.

Also I learned the hard way to never get your general involved in anything other than mopping up activities. Barbarian armies are totally undisciplined and if its an even battle will rout at the drop of a hat without the general.

Also I pick up barbarian cavalry whenever possible, the lack of cavalry is a huge disadvantage for Britannia, and I havent got them yet but hopefully the heavy chariots are better than the generals chariots.

The other problem I've run into is beating the German phalanx. I've managed to get a full cavalry charge on a phalanx units back while it was moving and the unit simply wheeled around pointed its spears at my cavalry and routed the whole lot of them. Phalanx's are kicking my behind I'd like some help with them as nothing i've done has worked so far.