An Iron Age highway preserved in peat
In 1984, workers harvesting peat in County Longford uncovered a massive wooden structure buried two meters down. This was the Corlea Trackway, an Iron Age road, or togher, built of oak planks. The acidic, low-oxygen conditions of the peat bog had preserved the organic material for over two millennia. The uncovered road is the largest of its kind in Europe.
The main trackway was at least 1 kilometer long and about 3.5 meters wide, large enough for wheeled vehicles like carts or chariots. Its construction was an impressive feat of engineering. The builders laid split oak planks, each 3 to 3.5 meters long and 15 cm thick, across parallel birch rails spaced about 1.2 meters apart. Archaeological analysis estimates that the main planks alone required felling 300 large oak trees. The entire project, including the smaller birch rails and foundation, would have required thousands of wagon-loads of timber. The trackway connected to a small island in the bog, from which a second, similar trackway continued for another kilometer.
Dated to a single year
Dendrochronology provided a precise construction date for the road. By analyzing the tree-ring patterns in the preserved oak timbers, researchers at Queen's University Belfast determined that all the trees were felled in late 148 BCE or early 147 BCE. The entire 2-kilometer roadway system appears to have been built in a single massive effort within one year.
The purpose of such a resource-intensive road is still being studied. It shows very little wear and sank into the soft peat within a decade of its construction, suggesting it was used for only a very short time. One theory proposes it was a ceremonial highway, perhaps connecting the ritual centers of Uisneach and Rathcroghan. Another possibility is that the construction itself was a ritual or a display of power, with the road's destination and longevity being secondary concerns. Whatever its function, the road was quickly swallowed by the bog, where it remained until its accidental rediscovery. Today, an 18-meter section is on display in a climate-controlled hall at the Corlea Trackway Visitor Centre.