Morris and his team believe the cellar, nearly 3m below the ground, was built in the second century. Several pieces of Roman pottery and coins were also found at the site.
The Romans built a fort around AD50 in Leicester, a settlement known as Ratae Corieltauvorum.
The dig was part of a multimillion-pound project to restore Leicester Cathedral, thought to have first been built in the 11th century.
The cathedral is now home to the tomb of Richard III, England’s last Plantagenet king and the last English monarch to have died in battle. He died in 1485.
The University of Leicester’s archaeological team found the medieval king’s remains a decade ago in a Leicester city centre parking lot. He was reinterred in the cathedral in 2015.