The Domesday Book. Twenty years after he had conquered England, William decided he needed a complete list of his possesions on this side of the Channel. It was to be a detailed account of the royal estates and those of his tenants-in-chief.
Since nearly all the country was involved, the result was rather like a present day census, though much more elaborate. It included facts about the population, the divisions of land, the houses, and so on.
But William wanted to see what changes had occured during his reign. Consequently, the investigator had to find out about the past as well as the present.
The result of this very complicated work was called the Domesday Book. All the evidence was given on oath; all the information was checked to make sure it was accurate.
The questioning was so thorough, that somebody said it was like Judgement Day (or Doomasdaya; it used to be spelt Domesday).
Among the uses of the Domesday Book were those of suggesting opportunities of raising more taxes, and of estimating the country’s military strength.
The latter was important. William was continually worried about the possibility of an invasion by the Danes.