progressively increased. The emperor Constantine in 332
allowed landlords to chain a colonus whom they suspected
was trying to escape, and from AD 365, coloni were not
allowed to sell their own property without their landlord’s
permission.
Just as we can use shipwrecks and the Greenland ice
cores to track the economic expansion of Rome during
earlier periods, we can use them also to trace its decline.
B y AD 500 the peak of 180 ships was reduced to 20. As
Rome declined, Mediterranean trade collapsed, and some
scholars have even argued that it did not return to its
Roman height until the nineteenth century. The Greenland
ice tells a similar story. The Romans used silver for coins,
and lead had many uses, including for pipes and tableware.
After peaking in the first century AD , the deposits of lead,
silver, and copper in the ice cores declined.
The experience of economic growth during the Roman
Republic was impressive, as were other examples of
growth under extractive institutions, such as the Soviet
Union. But that growth was limited and was not sustained,
even when it is taken into account that it occurred under
partially inclusive institutions. Growth was based on
relatively high agricultural productivity, significant tribute
from the provinces, and long-distance trade, but it was not
underpinned by technological progress or creative
destruction. The Romans inherited some basic
technologies, iron tools and weapons, literacy, plow
agriculture, and building techniques. Early on in the
Republic, they created others: cement masonry, pumps,
and the water wheel. But thereafter, technology was
stagnant throughout the period of the Roman Empire. In
shipping, for instance, there was little change in ship design
or rigging, and the Romans never developed the stern
rudder, instead steering ships with oars. Water wheels
spread very slowly, so that water power never
revolutionized the Roman economy. Even such great
achievements as aqueducts and city sewers used existing
technology, though the Romans perfected it. There could be
some economic growth without innovation, relying on
existing technology, but i