Rome wasn't built in a day. Rome known as the Eternal City was the first in the ancient world to reach 1 Million residents. Ancient Rome was the capital of an empire of ~70 millions inhabitants, but little is known about the ancestral origins of ancient Romans and expansion of Roman empire across ancient Europe, Asia and the Mediterranean region. Contemporary accounts and archaeological evidence indicated that with the expansion of empire, tight connections between Rome and other parts of the empire built through trade, military campaigns, new roads and slavery. However, those records provide limited information about the genetic constituents of the population. Ancient skeleton’s DNA samples and next generation sequencing technologies have been used previously to fill gaps in other regions of the world related to human history. Rome presented an interesting opportunity to use the same ancient DNA techniques and sequencing technologies to fill in details related to human history. Using ancient DNA and next generation sequencing technologies, an international team from US, Austria and Italy studied the genetic ancestry of individuals migrated through Rome since the Mesolithic period. In just few centuries the Roman Empire had expanded west to Britain, south into North Africa and east into Syria and Iraq. The study, published in Science, involved the sequencing of genomes of ancient individuals from various archaeological sites in Rome and other parts of central Italy spanning the past 12000 years. The investigators observed two major prehistoric ancestry transitions, one with the introduction of farming and other prior to the Iron Age. The sequencing data revealed individuals with ancestry from other parts of Europe, the Near East, North Africa, coinciding with trade and an increased movement of populations. Data also revealed a major shift in the Neolithic between hunter gatherers and farmers. Before founding of Rome, the genetic composition of the region approximated that of modern Mediterranean populations. During the Imperial period, there was net immigration from the Near East, followed by an increase in genetic contributions from Europe.
To accomplish the research goals and to find out what the genetic makeup looked like, investigators extracted DNA from the 127 powdered petrous bone samples. The bone samples were collected from 29 archaeological sites in Rome and central Italy and dated a few hundred years to 12000 years old between the Stone Age and medieval times. The isolated DNA samples were processed and sequenced using next generation sequencing technologies. The ancient individuals represented Mesolithic, Neolithic, Copper Age, Bronze Age, and Iron Age period. The individuals also represented the Roman Republic, Imperial Rome, Late Antiquity, and Medieval Period. The DNA sequencing was done at an average depth of just over 1-fold. The analysis of sequencing data resulted in broad genetic clusters aligning up with hunter-gatherers, early farmers, and post-Bronze Age individuals. Highly variable ancestries were observed for Iron Age individuals suggesting migration from multiple places into the region during this period. Data analysis revealed that Iron Age individuals genetically resemble modern European and Mediterranean individuals and display diverse ancestries as central Italy becomes increasingly connected to distant communities through new networks of trade, colonization, and conflict. The investigators also detected ancestry from Near Eastern populations and migration from other parts of Europe. Genetic changes reflected the gene flow from across the Mediterranean, Europe and North Africa. The authors state that "These high levels of ancestry diversity began prior to the founding of Rome and continued through the rise and fall of the empire, demonstrating Rome's position as a genetic crossroads of peoples from Europe and the Mediterranean". In future, the researchers plan to expand the geographic range of ancient DNA samples that would allow them to answer how ancient populations mixed and moved around. The team also plan to study the evolution of traits like height, lactose tolerance and resistance to diseases such as malaria.