The Redbridge viaduct between Tweedbank and Galashiels has been closed so that work, linked with the Borders Railway, can be carried out.
A popular footpath which runs over the bridge will also be closed, meaning a diversion of a mile for the people who use it.
Hugh Wark from Network Rail said:"We know that the Redbridge Viaduct link between Langlee and Tweedbank is an extremely popular walking and cycling route and we've done all we can to retain that access until now.
"The improvements we're making to the bridge mean that this relatively short eight week closure is unavoidable - we apologise for the temporary inconvenience.
He continued: "The bridge itself is in excellent condition and the structural works required are minimal. Once complete, this grand old structure will form another iconic landmark on the Borders Railway route."
Safety on the A7 was the overriding focus of a meeting at Falahill earlier this week between local MP Michael Moore and key organisations in the construction of the Borders railway.
Mr Moore convened the meeting at one of the busiest construction points and was joined by the Director of Environment and Infrastructure at Scottish Borders Council, the Network Rail Project Director, the Head of the Construction team at Contractor BAM and the local police inspector for the area.
“I have been contacted by numerous people about the state of the A7. This meeting with the most senior decision makers involved in the construction and monitoring of the railway saw all present make a commitment to safety above all else. Over the course of the meeting, we had an extended discussion about the issues of white line visibility, signage and traffic management. All present stressed that the liaison between Network Rail, the contractors BAM, and Scottish Borders Council, will be closer and more regular and road safety will be of paramount importance”.