The Germans will be a treacherous sort, so watch your back after Gaul is dead, or at least confined to Spain. Most of the time, those Germans attack me from behind. With a group of midsize armies containing Light chariots, Swordsmen (Chosen preferably), Head Hurdlers, Woad Raiders, Warband and Various Calvary Mercaneries, I just ripped through them like paper. The Romans, of course were different. You should amass large armies of what I stated above, plus dogs, other mercanaries, maybe some druids. Make sure you have a lot, becuase I led five armies onto the boot. One came from the North West, one from the North East, One from the South East (by way of boat) and the biggest one of them all landed right next to the Roma, herself. Using my navies, I cut off the Roman's income. I made sure to attack before the Marius reform so that I may still put extreme hurt to them via Light Chariots, Slingers and Head-Hurdlers. I wiped those Jullii right off of the boot (and the planet) with my blitz from the North, destryed the Brutti's section of Italy (leaving a few useless cities in Greece) and in about three years, after starving most of their soldiers and sabatoging their barracks, walls, et all, I sacked the eternal city. The key to Briton is to have lots of resources, or conquer a lot of places, because you must manage you money.