The Forth Bridge is to be closed for the first time in 70 years for essential maintenance work.
The bridge is one of Scotland's architectural wonders
Train services will be suspended for the next four weekends so that repair work on the structure can be carried out.
The line will be closed from 1159 BST on Friday until 0440 BST on Monday morning.
Long distance trains will be diverted via Stirling and Perth and extra buses will be scheduled to travel across the road bridge.
The 113-year-old bridge, which usually caters for 50 freight and passenger trains daily, has to be closed to allow extensive steel blasting and painting work to be completed.
It is part of an £11m programme of maintenance and refurbishment.
Experts insist the new paint will be the same unique red colour - but it should last a lot longer, at least 20 years.
The bridge was originally earmarked for closure last month, but that plan was abandoned because of a clash with pop star Robbie Williams' concerts in Edinburgh.
It will now be closed on all four weekends in July.
Bill Ure, director of the Rail Passengers Committee Scotland, said delays would be inevitable.
He said: "This is a short, sharp hit to get all the pain out of the way as soon as possible and we can see that this will deliver improved services."
Jim Bellingham, acting director of Network Rail, said: "We are aiming to strip back and paint up to 1,500 square metres of steel on the structure, working throughout the day and night where possible, to make the most of the access time we have when not trains will be running."
The bridge's design continues to inspire budding engineers.
Professor Roland Paxton, of Heriot Watt University, said: "At the time it was built, it was the best technology available to meet the engineering parameters.
"At the time there was tremendous pride over this Scottish achievement which was and is regarded by Scots as the eighth wonder of the world."
The 1.5 mile long cantilever rail bridge, which opened in 1890, crosses the River Forth between South Queensferry and North Queensferry.