How did Roman road builders know which way to go? If they were a few degrees out setting off from, say, Chichester, they could have ended up in what is now Slough, not London.
Tim Lewis
Narberth, Dyfed, UK
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At sea, the Romans used the North Star for direction, but on land, a series of beacons and a surveying instrument called a groma, comprising a staff with four plumb lines, were used.
Having set a beacon in Chichester, the surveyor would head off towards London, find a high point where the beacon could still be seen, set another beacon, and then would continue in this way with more beacons towards London. A groma was then used to line up the beacons, often moving them some distance until a straight route was achieved.
Robert Entwistle
Hon. editor of Itinera: The journal of the Roman Roads Research Association
This question nagged at the back of my mind for years, as the Romans had no magnetic compasses. In fact, most Roman roads weren’t laid out in the precise way of Stane Street – the road from London to Chichester. They followed a series of approximations to reach their goal, visiting relevant locations along the way.
The answer to why Stane Street is so precise is proposed in my book Britannia Surveyed. Soon after the Roman conquest of Britain, military surveyors planned a number of long, straight alignments (or traverses, in modern surveying jargon) from various key locations, as a way of understanding and mapping the new province.
Some of these traverses were used to establish locations for forts or military bases, and the military base that preceded Chichester was one. Sections of traverses were also later used by road builders (as the surveying had already been done).
Thus, Stane Street wasn’t surveyed to lead directly from London to Chichester. Chichester was instead built on top of a Roman base that was on a line surveyed from the crossing point of the Thames (which became London). In other words, Stane Street simply followed part of an established alignment.
The line came first – the locations and road afterwards.
Hillary Shaw
Newport, Shropshire, UK
The Romans often straightened pre-existing trackways, which may not have been so crooked anyway. Ireland, where the Romans hadn’t much influence, has some very straight roads. And Watling Street, the Roman road from London to Shrewsbury, isn’t totally straight, but is a series of straight stretches set off from each other at angles.
Pre-Roman roads, often pilgrimage or trade routes, had to cross pinch points like rivers at easily forded locations, or go to sheltered bays where sea trade came and went. With a largely empty landscape in between, each section could be fairly straight anyway. Subsequently, these points acquired military or trade roles because people had to pass there, so forts and towns began to grow up.
Both London and Canterbury began at easy fording points of their respective rivers, the Thames and the Stour, and Chichester was a well-sheltered pre-Roman natural harbour. The conquering, colonising Romans simply adopted the existing landscape, its towns and the straight-ish earth tracks between them, and developed these with their innovations such as baths and even straighter paved roads.
Bart Bols
Scherpenheuvel-Zichem, Belgium
The Romans had a law that required straight parts of roads to have a certain width, and that value was doubled for sections with turns and curves. This made turns far more expensive to build, sometimes to the detriment of the road’s effectiveness.
Roman roads are known for having gone straight up and over sizeable hills, when a slight curve around said hill could have made them far more manageable.
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