Thread by @jkpritch

Delighted to share our latest work, on ancient DNA of individuals from in and around Rome, spanning the last 12,000 years. At its peak Rome was the largest city of the ancient world with 1M inhabitants, controlling an empire of 70M people
science.sciencemag.org/content/366/64…

This was a wonderful collaboration with Ron Pinhasi and Alfredo Coppa; work was led by amazing people in my lab: @antmarge, @ziyue_gao, @mootspoints and other fantastic collaborators: @gaspi60 @ersilia_maria @diegoisworking @daniMfernandes @SerenaAneli @danjcotter @bigskybioarch

We sequenced 127 genomes, from 29 archaeological sites in Rome and central Italy. These span from the Mesolithic to the Medieval period. We see two major population transitions, corresponding to influxes of Neolithic and Steppe ancestry, as seen elsewhere in Europe.

Things get interesting from the Iron Age onward, timeframes that have been less studied elsewhere. Starting from the Iron Age, the population starts to approximate modern European/Mediterranean populations. But we continue to see marked shifts in ancestry.

These ancestry shifts indicate extensive immigration from different regions at different times--enough to dramatically shift the makeup of the Roman population. During the Imperial era, when the empire was at its peak, there was huge immigration from the eastern Med & near East

We know that during the Imperial era Rome was trading throughout the empire, as well as bringing back slaves, but we see few individuals with European or north African ancestry (2 each out of 48 total). These signals may reflect much higher population densities in the east

But in the following centuries, the Roman empire started to break apart, and split into eastern and western halves. At the same time, Rome's population collapsed from 1M to 100k individuals and was attacked by Visigoths and Vandals from northern Europe

During this period there was extensive immigration of European ancestry, shifting the overall makeup of Rome's population. In these plots, the blue labels indicate samples that provide an adequate fit for the incoming genotypes (by qpADM); note uncertainty about exact sources

Another point that was striking was the extent to which Rome's population was a mix of different ancestries living side by side. This goes all the way back to the Iron Age.
Clustering individuals with Chromopainter we found only modest clustering by time period after Iron Age

These data give us a sense of ancient Rome as this very cosmopolitan melting pot, with people coming in from around the empire--but with the rates from different locations varying dramatically by time.

Here's a cheat-sheet summary of the study:

Again, thanks to our many amazing Italian collaborators led by Alfredo Coppa; Ron Pinhasi's fantastic ancient DNA lab in Vienna; and Margaret Antonio, Ziyue Gao and Hannah Moots who did phenomenal work in my lab