William the Conqueror taxed England by swearing local juries to landholdings

Twenty years after the 1066 Norman Conquest, William the Conqueror's government still could not tax England accurately: land had changed hands repeatedly since the conquest, existing records were incomplete or contradictory, and any assessment based on landholders' own self-reported wealth was vulnerable to systematic understatement, since every lord had a direct financial incentive to declare less than he actually held.

Rather than continue taxing off unreliable self-reports or outdated pre-conquest records, William commissioned a direct, kingdom-wide survey — but built it so no single party's word, including his own officials', could stand alone as the record.

In 1085-86, William dispatched seven or eight panels of royal commissioners across England, each covering a group of counties, to record land, livestock, and value for essentially every manor in the kingdom within about a year.

Sent royal commissioners to convene sworn local juries, cross-examining testimony against lords' claims, so no single self-report could stand unverified.

Lords had incentive to understate, so self-reports were unreliable.

Local juries had knowledge but no stake in a specific lord's understatement.

Sworn testimony under perjury penalty made false claims costly.

Cross-examining conflicting accounts and comparing 1066/1086 caught discrepancies.

When self-reports are unreliable, gather data via independent local witnesses whose testimony is cross-checked and sworn under penalty.

The resulting Domesday Book delivered the most comprehensive, verified survey of a kingdom's wealth and landholding anywhere in medieval Europe, completed within roughly a year for a population of over a million people — an extraordinary administrative achievement for the era, and one that gave William's government a durable, cross-checked basis for taxation that self-reported records could never have produced.