Cheshire West & Chester Council has moved archaeologists onto the former Odeon cinema site to carry out exploration of land to be used for the foundations of Chester's theatre and library venue.
More than twenty trial trenches will be dug within the Odeon building itself, the basement of Commerce House and two adjoining properties in Northgate Street.
The project will take at least a month and will help determine whether structural foundations will have to be specially designed to preserve any important finds which may be made.
A section of sandstone wall, thought to be part of a mediaeval town house, has been discovered near the Odeon's boundary with Hunter Street, as well as fragments of Roman and mediaeval pottery in several trenches.
The theatre site lies in the Northern part of the Roman fortress and its footprint overlies an area that included barrack blocks and accommodation, which could have been part of the governor's enclave.
Mike Morris, historic environment project manager, specialist environmental services, for Cheshire West & Chester council, said: "It is early days yet but whilst these are research excavations, the location suggests we will add to our knowledge of Chester's past.
"The trial trenches are designed to save valuable time later on by giving us an early warning of potential special requirements now."
Work on the project has continued despite the Arts Council's recent decision to reject a funding bid of £5m.
Both project director, Graham Lister, and culture and recreation executive member, Cllr Stuart Parker, gave assurances that the project will go ahead, but the council is yet to reveal any sources of replacement funding.
Cllr Parker said: "The excavations will provide the knowledge that structural engineers will need to plan the foundations for this development."
Lister said: "This will be a theatre for every section of the community in West Cheshire. It has a tremendous fund of goodwill and £29m in the bank. We will build on both these tremendous advantages."
An archaeological desk-based assessment report on theatre site was undertaken by the council's Historic Environment Service earlier this year.
The report concluded: "The foundations of Folliott House and Commerce House undoubtedly damaged archaeological remains in these areas but significant remains probably survive beneath and around both of them.
"The concentration of buildings in this area highlights the complexity of the potential archaeological remains.
"There is a high potential of encountering Roman remains which would be of national significance."
London-based specialist architects Bennetts Associates have designed the £40.5m redevelopment.
The complex will occupy a one-acre site currently housing the former Odeon Cinema, Commerce House, its car park and 49 Northgate Street.
It includes a multi-functional theatre suitable for both presented and produced work, a studio theatre, fully integrated central library, rehearsal and dance studios, a café bar and public meeting areas.
A planning application was originally expected to be submitted this summer, with site preparation work scheduled to begin in spring 2014.
Indicative building costs are estimated at £33.8m for the theatre, £5.4m for the library and £1.35m for the cinemas.