Asclepius said:
I think you'll find I said only three legions were ever active at one time in Britain. Obviously the Danube was well defended but the comparison is still valid, 4 legions were in Pannonia and 5 were in Moesia stretched along a huge frontier from Singidunum to Troesmis. If Britannia were unimportant why bother stationing so many troops and rotating fresh troops at regular intervals?
1)9 legions along the border alone is over 45,000 soldires alone, combine this with a similer numbe rof auxilliaries, and you have 90,000 troops- take in the style of Roman deployment along this frontir, and it dwarfs in every respect the 30,000 troops total that Britian may have had
2)again, the importance of britian was primarilly political; Claudius needed as easy conquest to buffer his reputation with the army, and to win the love of the people- an adventure to the mysterous islands of the west, last bastion of the Celts was the perfect target- the peoples in it werent particuarly hard to fight, the Roman army already having adapted to such tactics, it had justifacation, and it had the bonus of being able to do what Julius caesar didnt- however, once you break it, you buy it, and the politics in Rome didnt support a weak leader- and no sign of weakness would be greater then giving up a Roman conquest, and its born out as until the last centuries of Roman rule, after the Government of the principate had long falled
(the principate refers to the government of the early empire, and how it was essentially a constitutional monarchy, for the observers of the thread) that only the Emperors most popular with the army that got away doing this (IE; Hadrian and Aurelian) Once it was conqored, it would have been political suicide to give it up, and thier was no particuler reason to do so- true Britian wasnt the most important of provinces, but if thier was pressing need to consider giving up an unimportant province, then why consider it- and Hadrian sealed the comitiment of Rome to keep all the provinces that existed, even those backwaters like Britian.