http://www.archaeology.co.uk/books/vindolanda.htmhttp://www.vindolanda.com/http://www.roman-britain.org/places/vindolanda.htmThe 208-212 problems in Britain was "solved" by the Emperor Severus, after his rule, there is no problem in Britain till the 400s. Now this solution is Britain SOUTH of Hadrian wall, a marginal Roman province. The Roman's did NOT have the heavy plow. There is some evidence of the heavy plow existing in Roman days in Asia Minor, by no movement of that plow into the Balkans or Western Europe till the Slavic invasions of the sixth century (500s). The majority theory, at the present time, relates the Heavy plow to China and the much superior Chinese Iron production methods that only reached Europe at the same time as the Slavic invasions.
More on Chinese Iron production:
http://www.staff.hum.ku.dk/dbwagner/koreanfe/koreanfe.htmlhttp://en.wikipedia.org/wiki/History_of_ferrous_metallurgyThe Heavy Iron Plow permitted farming in areas where you had below freezing temperatures, something difficult to do with Mediterranean farming techniques (Popular in Italy, Greece, southern France, Spain, North Africa and the rest of the Mediterranean world). Thus in Roman Days, it was almost impossible to farm north of about Paris, thus farming in England was either spade work (and given that most spades were made of wood, not that popular) or grazing of cattle. Grains would be imported in exchange for meat, Copper ore, other ores, horses, Oxen and timber. Rome only occupied Britain to secure its access to tin, thus all of the Roman Units in Britain were occupations units with local "allies" (i.e. paid off locals who supported the Romans against their own countrymen, just like in Afghanistan and Iraq today).
It appears the Hadrian Wall was more to keep people IN Britain then to keep people out (The comparison with the Berlin Wall was made in the 1980s, do to excavations on the wall would indicate the wall main "defense" was against movement from the SOUTH not the North and based on those defenses, most archaeologists would have said it was a wall to Defend Scotland from England (To use later names for both areas, the Scots did not move into Scotland till after 500 AD, and the Angles (later English) did not move into southern Britain at about the same time) NOT to defend England from Scotland.
Recent research seems to indicate the purpose of the Wall was to keep people IN not to keep people out. i.e like the Berlin Wall not the Maginot line. These "Refugees" appears to be people from present Day Scotland, based on the type of housing they built, thus may be evidence of massive movement north of people living in Present day England, who displaced people in present day Scotland as they ran away from what ever level of slavery or Serfdom they were living under in present day England. The Celts in Present day England, moved to Scotland to get away from Severus, disputing the rule of people in present day Scotland. The people of present day Scotland went to the Romans on the Wall and asked for support, support they have been getting for centuries as the Romans asked them to help them keep the peasants in present day England and Wales, by returning them to their Roman Masters. This time the escapees were to many, so the allies had to seek shelter from the Romans. After a few years, the Allies were sent back to present day Scotland where they either defeated the comers, or made a deal with them (The Third Century AD was a rough century for the Roman Empire, it almost fell at that time, the Empire Survived, but it was no longer the military super power it had been, not even the sole super power (The Persians had gotten their act together so for the First time since Alexander the Great could and did challenge Rome, This was the result of another act of Severus, his attack on the Persian capital, which lead to the overthrow of the Parthians the their replacement with a more Centralized, united and powerful native Persian rulers).
Severus's rule has been called the first indications of the Fall of the First Roman Empire, an empire founded during the Republic with the Rule of Marius and Sulla of about 100 BC (Rule by the elite of Roman Society and its Senate) to be replaced by the Second Roman Empire of Diocletian and Constantine (An Empire much more like a Republic, but with a strong leader). The Second Roman Empire differed from the first, in that it viewed the Empire as a whole as one Country (Romania, a term that became the norm in referring to the Roman Empire after the problems of the Third Century) as oppose to the City of Rome (and maybe Italy) and its subject provinces (Which had been the thought pattern of the Last Roman Republic and the First Roman Empire).
Britain came under this change of concept and the abandonment of Britain in 410 AD, was by the Roman Army NOT the Roman Government (Which included the Catholic Church by that time period) thus Britain stayed "Roman" for decades after the Roman Army left and decades after the abolishment of the Western Roman Empire in 476 AD (Which was characteristic of much of the Western Empire). England only became English do to the subsequent conquest of England by the Saxons and Angles (Which, unlike in the agriculture parts of Empire, the population was low compared to the Germanic invaders, thus it was possible for invaders to replace the lower populations natives, this was aided by the fact one Slavic tribe reached Britain in the late 500s and with it brought the heavy iron plow, which permitted the invaders to out populate the Natives, something impossible south of Paris).
Just comments on what this may be and note on the historical context of this movement.
One last comment, about 200 AD, it is believed the Dark Age Cold Period started (and this seems to be the cause of the Movement of the Germanic Tribes and later the Slavic Tribes). This movement in-testified in the Fifth Century, so all of the marginal agricultural land of the Roman Empire were becoming even more marginal as time went by. The Slavic invaders with their heavy Iron Plow were the only "barbarian invaders" that could maintain agriculture or re-introduce agriculture (or even introduce agriculture) to these increasing areas of marginal farm lands. Thus had the effect of driving deep into the Balkans (including mainland Greece) and pushing the Germans to the Elbe (The Elbe seems to be the border between Germans and Slavs around 900 AD, the Germans then pushed back the Slavs till Poland formed up around 1000 AD).
Thus the Heavy Iron Plow may be the reason Europe did as well as it did in the Dark Ages, it survived, something the people of present day Scotland would have had a much more difficult time during in the 200s AD.