Essential maintenance work to the grade II listed Middleham Bridge, on the A6108 near Leyburn, is due to take place this week.
The County Council bridges team will be repointing part of the northwest turret where excess movement at the join between the parapet and the turret has caused the mortar to crack.
Councillor Karin Sedgwick, member for the Middle Dales division, said: “In recent years Middleham Bridge has been used and admired by people around the world during the Tour de France and UCI World Championships, and is very popular with tourists.
It is vital we keep this historic structure in the best possible condition.
“We appreciate that the closure and lengthy diversion will be an inconvenience for many but ask the public for their patience while the maintenance is being carried out.”
Work will begin on Monday, July 5 and will last for three days.
During the working hours of 8am to 6pm the bridge will be closed to road users and pedestrians. Emergency vehicles will have access.