It's one of Wales' best kept secrets, a piece of living history that's right beneath our feet.
An ancient Roman road running throughout the length of the country, from Conwy in the north to Carmarthenshire in the southwest, Sarn Helen is a unique, semi-hidden wonder.
One of the most well-preserved Roman roads in Wales, its cobbled stone remains are exposed for all to see in certain places, uncovered thanks to many centuries of wear.
Read more: You can find more history and nostalgia stories like this here.
A popular route for walkers - some of whom claim you can almost hear echoes of the Roman boots that once trudged along it - Sarn Helen was built nearly 2,000 years ago.
It's named after the Celtic princess Elen Lwy-ddawg - or Saint Elen, an early founder of churches in Wales - who was married to Magnus Maximus, the feared Roman emperor who arrived in Britain in about 368AD.
The daughter of the Romano-British ruler Octavius, it's believed it was she who persuaded her husband to build roads across the country so that his soldiers could more easily defend it from attackers.
Legend has it she was also married to the infamous wizard Merlin and great mysteries still remain about the large standing stones - some measuring 13ft high and considerably pre-dating the Roman occupation of Britain - which can be found along particular sections of the road.
One, in particular, known as Maen Madoc, still bears the ancient Latin inscription which reads, 'Dervacus, son of Justus. Here he lies'.
Found within what's now known as the Brecon Beacons National Park, it's perfectly aligned with the area's largest standing stone - Maen Llia - which is located at the head of the Llia Valley.
Indeed, were it not for forestry standing between the two stones, you could clearly see one from the other despite them being some two miles apart.
Maen Llia is thought to have been erected in the Bronze Age, and considering that a quarter of the stone lies buried deep within the ground, the effort to place this great stone would have been immense.
And debate still rages around what these stones are meant to indicate, with academics arguing over whether they're primitive route markers, Stone Age territorial signs or gravestones marking burial caverns of those who died at the roadside.
But, while the theories surrounding them remain as well-worn as Sarn Helen itself, the truth will likely always remain just below the surface, tantalizingly out of reach.
To get the latest email updates from WalesOnline click here.
