More than 3,000 skeletons are being excavated from a burial ground used during the period of the Great Plague in 1665.
The Bedlam burial ground is at the site of the new Liverpool Street station that will serve the cross-London Crossrail line.
Used from 1569 to at least 1738, the burial site was also known as Bethlehem and the New Churchyard.
Tests on excavated plague victims will further understanding of the evolution of the plague bacteria strain.
A team of 60 archaeologists will work in shifts, six days a week to remove skeletons and carefully record evidence for what may prove to be, in archaeological terms, London's most valuable 16th and 17th-century cemetery site.
The skeletons will be excavated over the next four weeks, after which archaeologists will dig through medieval marsh deposits and Roman remains.
A Roman road runs under the site, which has already yielded several interesting Roman artefacts such as horseshoes
and cremation urns.
Archaeologists are expected to finish on site in September, after which construction will proceed on a new eastern ticket hall by contractor Laing O'Rourke.
Crossrail lead archaeologist Jay Carver said: "This excavation presents a unique opportunity to understand the lives and deaths of 16th and 17th century Londoners.
"The Bedlam burial ground spans a fascinating phase of London's history, including the transition from the Tudor-period city into cosmopolitan early-modern London."
He went on: "This is probably the first time a sample of this size from this time period has been available for archaeologists to study in London.
"Bedlam was used by a hugely diverse population from right across the social spectrum and from different areas of the city."
To date Crossrail has found more than 10,000 artefacts spanning many years of London's past across more than 40 construction sites. It is the UK's largest archaeology project.
Preliminary excavations at the Liverpool Street site in 2013 and 2014 have already uncovered more than 400 skeletons and numerous artefacts.