A section of the Ridgeway near Avebury will remain closed to cars and motorbikes for an extra 21 days while it recovers from severe winter weather.
The byway from Green Street to Hackpen Hill in the heart of the World Heritage Site is still affected by deep ruts and standing water.
It was due to re-open for the summer on 1 May, but Wiltshire Council has introduced a three-week prohibition of driving order to give it more time to recover.
The order may be extended by an extra 21 days if necessary.
The stretch will remain open for walkers, horses and cyclists but closed to motorbikes and motor vehicles apart from emergency services and landowners.
Bridget Wayman, Wiltshire Council’s cabinet member for highways, said: “The weather in recent weeks has left the surface of the byway severely rutted, and it is still holding water in numerous locations.
“There are globally important archaeological features on and immediately below the surface and they need to be protected from further damage.
“We apologise for any inconvenience this may cause and would like to thank the public for their understanding and co-operation.”
The entire Wiltshire stretch of the Ridgeway National Trail is already subject to an annual prohibition of public motor vehicles from 1 October to 30 April to protect it from damage.