Work has begun to remove a limestone sarcophagus unearthed at Lincoln Castle, which may contain the remains of a "Saxon king or bishop".
The unopened box, thought to date from AD900, was found by archaeologists alongside the remains of a previously unknown church earlier this year.
An examination with an endoscope revealed it contains human remains.
Project manager Mary Powell said removing it from the ground was a "delicate" operation.
She said that the sarcophagus, which is buried about 3m (10ft) underground, would need to be slid out horizontally in order to preserve it.
"We know there is a hairline crack in the lid and we don't want to do any damage - we want to get it out as intact as we possibly can."
She added that she hoped the lid would reveal the identity of the person inside the sarcophagus, which may also contain gold alongside the remains.
"There might be nothing carved on it, but it would seem likely [that there is]," she said.
The dig was undertaken as part of the £19.9m Lincoln Castle Revealed project, which will see the building of a new centre to house Lincoln's Magna Carta and a tower to provide access to the castle walls.
The project is due to be completed in 2015, when many of the finds from the dig will be put on display.