The demand and need for fish was matched by the demand for salt. Salting meat was one of the few ways open to people to preserve foodstuffs and so was a very important product.
There are some well-known and famous salters’ roads in England where there has been more rigorous research of the medieval road network than in Scotland. The Cotswold Saltway is known to have been used as long ago as the eighth century Clennel Street in Scotland is the northern part of a huge route from the Northumberland coast, through Rothbury and Alnham and along the high Cheviots to the Scottish border and then onwards by Clennel Street.
Producing salt involved pumping seawater into vast pans and firing coal to boil the water off and leave the salt crystals behind. It took almost 32 tons of seawater to produce one ton of salt and boiling off the 31 tons of water required the continual firing of roughly 9.5 tons of coal over a period of 22-28 hours. Scotland had no salt mines or salt springs and so desalination was the only way to produce it. The process was very labour intensive and required so many raw materials that salt was a very expensive commodity and only available to the wealthy.
It is also no coincidence that salt pans were closely linked with coal mines. Nowhere in Scotland is this connection clearer than in Culross where George Bruce worked the nearby coal seams while using the coal not exported to produce salt also for export.
The routes used by these salt traders have been dated as far back as the dark ages in England but the furthest back we can date them in Scotland is the mid medieval period. The evidence for that is based on the age of the institutions the route serves rather than archaeological evidence of the route due to a lack of research into these important trading routes.