I see I spelled Tiberius' name "Tiberias".

>>My only idea is that any general good enough to conquer Germany was an instant candidate to replace the sitting emperor.<< There was also a question of military strength and international balance of power. I have read that the legions destroyed in Teutoberger Wald were never replaced. They couldn't recruit and train enough troops. They would have to strip the rest of the empire for formations to retake Germany. The Parthians were a constant threat to the Romans' eastern provinces. Weakening the Parthian frontier would be an invitation to a Parthian invasion of Rome's most prosperous possessions. Caesar Augustus was no military genius, but he was a pretty good accountant.

I have read there were three legions lost in the Teutoburger Wald. When the Cimbri and Teutones showed in the vicinity of Italy around 114BC, the republic lost five consular armies (100,000). Rome was able to recover its losses in time for Marius and his colleage to defeat them. In the Hannabalic War, Rome was able to recover from the battles of Trasimene (15,000 lost) and Cannae (80,000 lost according to Polybius). In AD 9 legions would have a nominal strength of 6,000 which would mean Varus' legions lost at the Teutoburger Wald would be 18,000 give or take. Did the Romans fail to reconstitute the legions out of a lack of man power or did they retire the legionary standards of these legions for them to be a memorial to the dead? The legionary standards were recovered by Rome later. Where did you read about the Roman Empire not being able to train and recruit enough troops? I knew Italy became less and less a recruiting ground but the empire more than made up for that with legions manned by provincials.

Tacitus, in his "Germania" described the Germans as being much more a threat than the Parthians.

>>Where did you read about the Roman Empire not being able to train and recruit enough troops?<< I first read about it in Liddel Hart's "Military History of the Western World". I've read it in other histories as well, but I can't remember them off hand. >>I have read there were three legions lost in the Teutoburger Wald. When the Cimbri and Teutones showed in the vicinity of Italy around 114BC, the republic lost five consular armies (100,000). Rome was able to recover its losses in time for Marius and his colleage to defeat them<< The Roman Legions were enlisted short term service before Marius, or rather for the period of state emergency. The majority of Roman population consisted of smallholding farmers. These smallholders were the recruiting base of the army. The long Punic Wars bankrupted the smallholders. They could not work their farms and they were not paid while enlisted. Their farms were bought by large senatorial families and worked with slaves. This decimated the army's recruiting base. Marius transformed the legions into paid, long-service, professional formations. It helped keep veteran troops off the streets, but it didn't rebuild the recruiting base. I'm going to use the Marine Corps as a simile, because that's what I'm familiar with. The Corps has as a strength of roughly 170 to 180 thousand. Recruiters don't have to deliver 170,000 new Marines every year, only 30 to 40 thousand (enough to maintain authorized strength). If we lost half the Corps in a disasterous war the recruiters would have to deliver 85,000 new Marines (roughly equal to the Army's yearly need), plus the 30,000 or so to cover normal attrition. On top of that, the reconstituted formations would be less effective for years until they were trained up. This is the problem that Augustus' "recruiters" faced.

Attrition of a recruiting base would explain why the Roman army would not be able to get enough soldiers into the legions. I have read about what happened to the family farms in the Hannibalic War. It was either Edward Gibbon or H.G. Wells who wrote that the freeholders migrated to the cities. He wrote that their only available livelihoods were as artisans catering to the tastes of the rich or as soldiers in the army. From that I assumed there was a big windfall for Roman army recruiters. Unless the people from the countryside stopped having children or left Italy or preferred civilian employment I wonder what made them unavailable to the army recruiting base.

"I wonder what made them unavailable to the army recruiting base." Read on in your historys. An increasing portion of the freeman population of Italy became slaves. The wealthy landholders became loathe to give up any of their precious labor.

The cricial turning point is the defeat in Teuteburger Wald (near Osnabrück) where XVII, XVIII and XIX legion perished, never to appear again in the Roman army list. At that time these legions must have been recently raised (their numbers high and in sequence, Yes I know that sequence was not strictly held and there were doublets of numbers, hence cognomen) Which means about 10-20% of the regular Roman army was destroyed. The mission of Varrus was originally a resonably pacific civilising mission. The sensible conclusion of Augustus was that the cost and risk to the empire vastly outweighed the uncertain benefits. Limiting the Empire behind the Rhine and the Danoube (the right bank of which is particularly difficult to scale at most places) - very defensible lines was another great benefit. The Roman Empire would recieve little benefit from including the wild tribes in the Empire, and the problem of keeping them in check - though always a problem - was soluable. Teuteburger Wald was one of three major disaters of the Roman Army, the other were Crassus defeat against the Parthians and the third the raising in Palestine - not in 79 - in about 123, where the Empire took that country apart, and the jews went into diaspora. Hope this clarifies.

How did the free men become slaves?

By roman law if you can not pay your debts you became a slave. Also do not confuse the Rebublican Roman army with the Imperial Roman Army. The Republican army was a militia force. Imperial one was a professional. It is far expensive and train a professional force. Of course in the end you will have a force that can defeat an army several times of its size.