Wat Dyke's Heritage Trail stretches between mid and north Wales
A 60-mile (96.5km) path following the route of an ancient dyke, which may have been built 1,500 years ago, is being opened.
Wat's Dyke Heritage Trail between north Powys and Flintshire has been nearly nine years in the planning.
There are conflicting opinions about when the earthwork was built, but it could have been the 5th or 6th Century, pre-dating Offa's Dyke.
The trail will be opened by Environment Minister Jane Davidson near Wrexham.
The path uses public footpaths, bridleways and quiet country lanes between Llanymynech, near Welshpool, and Greenfield near Holywell.
The trail also strays over the border into Shropshire, passing the town of Oswestry before making its way into north Wales.
The Wat's Dyke Association said it was a mystery who built the earthworks and whether it was an agreed boundary or a military fortification in a disputed area.
Speaking ahead of the official opening, Ms Davidson described the path as a "remarkable achievement" that would bring historic, leisure and economic benefits to a number of areas.
Wat's Dyke Association chairman, Ron Williams, thanked those who had helped make the trail a reality.
He added: "It has taken a long time but at last it's officially open and I hope it will prove popular with walkers and local residents along the route and I hope it brings many benefits to the area."