Work to create a 68-space car park next to Witham rail station may be delayed because the site was once home to an Iron Age settlement.
Braintree Council completed the purchase of Eckard House, in Easton Road, last month.
The area was once the site of a three-storey office block, built in the 1970s, which was demolished in 2011.
The council has submitted an application to convert the land in a bid to ease parking problems for commuters, but an archaeological inspection has been demanded before building work begins.
Essex County Council (ECC) historic environment officer Teresa O’Connor said: “The proposed car park lies within the remains of a historic site known as Chipping Hill Camp."