…the Conqueror turns southwards and arrives at the Roman and Viking city of Lincoln.

When William reaches Lincoln (one of the country's major settlements), he finds a Viking commercial and trading center with a population of six thousand to eight thousand.

The remains of the old Roman walled fortress located sixty meters (two hundred feet) above the countryside to the south and west, proves an ideal strategic position to construct a new castle.

Also, Lincoln represents a vital strategic crossroads of the following routes (largely the same routes which influenced the siting of the Roman fort).

A castle here could guard several of the main strategic routes and form part of a network of strongholds of the Norman kingdom, in Danish Mercia, roughly the area of the country that is today referred to as the East Midlands, to control the country internally.

Also (in the case of the Wolds) it could form a center from which troops could be sent to repel Scandinavian landings anywhere on the coast from the Trent to the Welland, to a large extent, by using the roads which the Romans had constructed for the same purpose.

The Domesday Survey of 1086 directly records forty-eight castles in England, with two in Lincolnshire including one in the county town.

Building a castle within an existing settlement sometimes meant existing structures had to be removed, and of the castles noted in the Domesday Book, thirteen included references to property being destroyed to make way for the castle.

In Lincoln’s case 166 “unoccupied residences” are pulled down to clear the area on which the castle is to be built.

Work on the new fortification is completed in 1068.

It is probable that at first a wooden keep was constructed which will later be replaced with a much stronger stone one.

Lincoln Castle is very unusual in having two mottes, the only other surviving example of such a design being at Lewes.

To the south, where the Roman wall stands on the edge of a steep slope, it is retained partially as a curtain wall and partially as a revetment retaining the mottes.

In the west, where the ground is more level, the Roman wall is buried within an earth rampart and extended upward to form the Norman castle wall.