James of Saint George, a famous architect and engineer from Savoy, was probably responsible for the bulk of the construction work across the region. The castles were extremely costly to build and required labourers, masons, carpenters, diggers, and building resources to be gathered by local sheriffs from across England, mustered at Chester and Bristol, before being sent on to North Wales in the spring, returning home each winter. The number of workers involved placed a significant drain on the country's national labour force. The total financial cost cannot be calculated with certainty, but estimates suggest that Edward's castle building programme cost at least £80,000 – four times the total royal expenditure on castles between 1154 and 1189.