The graves found at the Gaillard Auditorium construction site may be older than previously thought.

Charleston Mayor Joe Riley said Friday it appears the 27 burial pits could date to the 1720s or 1730s, making them part of the earliest settlement times of colonial Charleston.

The discovery shows “we continue to learn” about Charleston’s history in unexpected ways, he said.

Based on where the graves were in relation to the 1700s center of town, Riley said the location was probably considered to be an isolated part of the settlement, or in the heavily wooded “outback.”

Riley’s comments came as the city announced the excavation and removal of remains will begin early next week. The move is widely seen as the first step toward determining who is buried there.

In the meantime, work is continuing at the $142 million Gaillard make-over, but in areas not affected by the dig. Riley said the graves removal, which is expected to take about two weeks, won’t greatly delay the timetable or increase the cost.

The discovery of the 27 sites came last week after workers were digging a trench toward Anson Street and unearthed a human skull. After a rain delay, the excavation resumed this week.

Lead archaeologist Eric Poplin said Friday he still believes the graves were part of a previously unidentified cemetery that either was forgotten or intentionally covered over as the city’s neighborhoods and streetscape grew.

Based on the pattern of the graves — in two mostly even rows — Poplin also believes the site was used by residents over a long period, not during a single interment that might be indicative of an epidemic.

“To me, (the rows) imply it was in use over time,” said Poplin, of Brockington Cultural Resources Consulting in Mount Pleasant.

So far none of the grave sites have been intentionally opened up. Some skeletal material near the surface has been exposed, but accidentally. A decayed nail, probably used to fasten a coffin, was also found.

Poplin and other workers uncovered most of the graves after opening a trench measuring about 70 feet long next to Anson Street. The graves, easily identified as rectangular brown and purple stains, were about 10 feet down under what previously was an asphalt lot.

Most of the work at the site slowed down Friday as Poplin used a surveying tool to map global positioning coordinates.

When the remains are removed, researchers hope to find out more about who they were and what may have killed them. Bones can tell sex and race, and also what diseases may have been present at the time.

No more graves beyond the 27 uncovered so far are expected. The remains are likely to be reinterred in a recognized cemetery.

Reach Schuyler Kropf at 937-5551.