As originally designated, it ran from the A15 at Bourne Market Place (TF095201), eastwards to Fleet Hargate, three kilometres east of Holbeach (TF393250), on the A17.

The main difference in the present case is that the road designation has been extended from the A15 at Bourne to the A1 at Colsterworth, while at the other end, the easternmost three kilometres have been replaced by a new part of the A17.

The last 1.6 kilometres of this road, as the trust left it, running down the hill to Bourne Market Place, are now part of the A151.

Its remit included the forerunner of the present A15 which crosses the end of the Stamford road at Bourne Market Place.

According to Cary's map of 1787, the official route ran via Tongue End (TF155188) and crossed the River Glen at Gurthram (TF173224).

The principal source of information about the positions of toll gates is the Ordnance Survey 1 inch map published in 1824.

He wrote of it thus: In the Hundred of Skirbeck to Boston, and thence to Wisbeach, [turnpike roads] are generally made with silt, or old sea-sand, deposited under various parts of the country ages ago, and when moderately wet are very good; but dreadfully dusty and heavy in dry weather; and also on a thaw they are like mortar.

What he is saying is that the turnpike roads in the Townlands were made of the same marine silt as forms the land itself in that part of the country.

The heaviness in dry weather to which he refers, arose from the loose, deep, sandy surface through which wheels would have to be dragged.

By the end of the 20th century granite and slag were being consolidated by steam roller[4] Of the Bourne to Colsterworth road, Young said we were every moment either buried in quagmires of mud or racked to dislocation over pieces of rock which they term mending.

It then passes across a gently sloping dissected plateau of Jurassic rocks capped in its highest parts by glacial clay.

Having for some time, extended its influence by diplomacy and trade,[j] The Roman Empire began to take control in Britain from the year 43.

An important part of the means of control was the building of soundly-built roads, running directly between key places.

The English successors of the Romans in Britain, called this road Ermine Street from their word for "soldier", compare the German personal name, Herman.

[m] The twenty kilometre length of Ermine Street, at roughly the centre of which, the line of the A151 lies, passed over chalky till (boulder clay) which is very sticky when wet.

As the Ermine Street carriageway broke up, people sought easier going by moving down towards the small River Witham whose valley had been eroded through the till, into the Jurassic limestone below it.

Three kilometres from the start, at the hamlet of Birkholme, the road finds a shallow valley formed by erosion which has cut through the till and exposed the underlying Jurassic limestone soils.

[q] The road follows this valley, under the railway main line, past the second toll gate site at the junction with the Boothby Pagnel road (B1176), then down to the River Glen at Corby Glen, where it turns a little southwards to avoid more glacial till and keep to the upper Lincolnshire limestone.

[r] The land between Colsterworth and the western edge of Bourne is a plateau, gently sloping down to the east and much dissected by erosion during periods when it was near but not under ice caps.

The surface dips very gently towards the east but the geological strata dip more steeply so that a kilometre out of Corby Glen, the road passes onto the strata above the limestone, known as the Upper Estuarine Series, the Blisworth Limestone, Blisworth clay, Cornbrash and Kellaways clay, in that order.

Once the semi-circular diversion is completed, the road turns sharp left again, through Grimsthorpe where it is on Jurassic clay.

Its present course is dictated by the former presence of Bourne Castle at the town end and by a desire to keep to the crest of a slight ridge in the hillside.

[x] It is towards the top of this section that it is possible to detect a change in slope betraying the former presence of a shore of the Devensian periglacial lake, which was impounded by the ice into the Fenland basin.

The market place was positioned immediately across a moat and a pomœrium, outside the gate but those are no longer visible from the road.

As the A151 reaches this, it turns back through 45° and continues eastwards along that approach road, across the line of the Roman version of the A15, King Street and past the Abbey Lawn.

At the edge of the town, it turns away from the now hidden river bed, almost eastwards across the black, humic soil of Bourne North Fen.

Roads on the black soils tend to crumble at the edges as the soft humus collapses and oxidises.

It is typical too, in that it rises and falls as it passes over the silt banks left amongst the peat by small to medium marine creeks from the Middle Bronze Age, 3 to 3½ thousand years ago.

It was a grange of Sempringham Priory on the site of the modern Mornington House round which the district boundary is still diverted as it was when the abbey, on the Kesteven fen edge, owned it.

of 1765 but this part of the South Forty-foot is a re-use of one of the main drains of the Lindsey Level, a scheme which was declared complete in 1638.