I came across some interesting thoughts on another thread:
https://bitcointalksearch.org/topic/peak-gold-how-the-romans-lost-their-empire-554616while I am researching a couple of ideas, I have some notes for reference:
"The Roman Empire grew through conquest. Subsequent conquests were financed by the spoils of the previous
conquests and the increased taxes from expansion. The conquests also financed the increasing size of bureaucracy
required to maintain an expanding empire."
True, up until Egypt was seized by Augustus, after that Rome preferred a defensible frontier, or
was forced into war by circumstances.
"Once the cost of maintaining the empire exceeded the returns from expansion, the empire stopped growing. "
The history is somewhat more complicated.
in AD14 Tiberius ordered Germanicus to the Northern extent of the Empire to put down a mutiny by the
troops overy pay. Once there Germanicus took the Army and the mutineers into Germany and plundered the
area as a reward to the Legions.
By 105AD Rome needed silver and gold to expand its monetary base, and to pay the Army. Trajan built a bridge
across the Danube, and plundered Dacia, also gaining access to the rich mines of the area.
In 272AD Aurelian went to war with the Palmyrene Empire to regain control of Egypt and the grain supplies
to Rome.
Hence while the statement is evidently true, the calculation of excess returns is at best, imprecise.
Also, after 167BC the costs ot the campaign were borne by their provinces.
"For example, administering the farthest regions of the empire became more costly
than the income from those regions, and some of them were abandoned. Conquering England brought less spoils
than the cost of that conquest."
Paying the Army on the frontier was always a loss leader, but it put Roman money into the local economy,
and financed the Roman lifestyle. Roman Monopolies always made the centre appear more affluent.
"At this point the empire began debasing the currency to compensate for the decrease in spoils and new
populations to tax."
I am uncomfortable with that statement. Arguably peace, technology and infrastructure, access to capital,
and the Roman economy increased wealth and GDP and thus the tax base.
"The empire also increased taxes and became more repressive."
For example, in 167BC, "Rome no longer needed to levy a tax against its citizens in Italy", so not
the whole story, but see below.
"The currency was so debased as to be practically worthless, but the empire still paid its military
and bureaucracy with it. Eventually the empire grew so weak it was unable to resist barbarian invasions and Rome fell".
Debased is not the same as worthless. The modus operandi following the accession of an Emperor was:
debasement to pay off the Army, thus delivering a stimulus to the economy and a spike in inflation, and
thereafter gentle deflation in the Emperor's lifetime. Over time, this probably caused problems with trade,
and I seem to recall that India wanted gold for spices and China wanted silver for silks.
The gold content of Roman coins was almost always of high purity [modern coins have some copper to
reduce wear], but the Roman silver coins went from 97 percent to 2 percent silver. My back-of-an-envelope
calculation shows a further complication: between 250AD and 270AD almost 90 percent of the silver
content of the coins in circulation may have disappeared. How much was hoarded, how much was stolen,
and how much was melted down for foreign trade is anybody's guess. In 271AD Aurelian slaughtered 7000
at the mint in Rome to end the fraud and the theft of silver.
From 250AD to 270AD trust in the currency weakened, barter became more frequent, and by 300AD even
the Military were paid in kind, resulting in the imposition of a reign of terror on the countryside.
"Peasants were so overburdened that some abandoned their fields and went to Rome for the dole, some sold children
into slavery, etc. The peasants were increasingly complacent to barbarian invasions and some welcomed barbarians
as liberators."
Again, not the whole story. See:
http://www.unrv.com/economy/roman-taxes.php"Large inflation rates and debased coinage values, by the reign of Diocletion, led to one of the more drastic
changes in the system. In the late 3rd century AD, he imposed a universal price freeze, capping maximum prices,
while at the same time he reinstated the land tax on Italian landowners. Special tolls on money traders and
companies were also imposed to help increase the tax collections.
Diocletion's program, in theory, should have helped ease the burden on various classes of taxpayers, but it
didn't work that way in practice. As an example, additional taxes were levied on land owners after the land tax had been paid because this was now a separate tax, instead of taking into account that taxes had already been collected. The burden of paying the expected amounts was shifted from communities and individuals within them, to the local senatorial class. The Senators who would then be subject to complete ruin in the case of economic shortfall in a particular region. Following Diocletion, Constantine compounded these burdens by making the senatorial class hereditary. By so doing, all debts and economic ramifications were passed from one senatorial generation to the next, ruining entire families and never allowing for a recovery that could benefit an entire community"
In summary, a much more confusing picture of the collapse. My belief remains that excessive debt was the
driver for the collapse, but the link between cause and effect remains elusive.