Built in 1820 and crossing the River Tweed four miles upstream from Berwick-upon-Tweed, the Union Chain Bridge was removed a year ago as part of a £10.5 million major renovation.
Engineers have already repaired all of its components and pulled the first of 13 chains into the water.
Once the remaining chains are in place, the deck hangers will be reinstalled and the bridge deck rebuilt ahead of an expected reopening later this year.
The 200-year-old structure is believed to be the world’s oldest vehicular suspension bridge still in operation and has attracted the attention of span enthusiasts and other visitors to the area.
Local authorities on both sides of the border, Northumberland museums and the Friends of the Union Chain Bridge community group have put together a package of funds for repairs, sparked by serious concerns about its condition.
Northumberland County Council Local Services cabinet member John Riddle said: “This is another milestone, and a very long awaited one, to finally see this iconic structure begin to come together.
“We have been working hard to keep as many of the original details as possible while also ensuring that the bridge can fulfill its primary purpose, and everyone involved in the project is delighted to see the bridge taking shape again.”
Gordon Edgar, executive member of the Scottish Borders Infrastructure, Travel and Transport Council, said it was “an extremely important project” that will protect “this historic structure for many, many years to come.”
The Union Chain Bridge was built by retired naval captain Samuel Brown and completed in 1820.
Building and replacing the “dangerous ford” downstream cost about £7,700.
Although work on Thomas Telford’s Menai Bridge in Wales had begun before him, the Union Bridge was completed first, making it the world’s longest iron suspension bridge when it opened.
Hundreds of spectators, including civil engineers Robert Stevenson and John Rennie, turned out to watch it open on July 26.
Until the 1970s, it existed with minimal maintenance, but in 1974 the entire deck was replaced.
Concerns about its condition have intensified in recent years, finally leading to a major overhaul.