William continued the collection of danegeld, a land tax. This was an advantage for William, as it was the only universal tax collected by western European rulers during this period. It was an annual tax based on the value of landholdings, and it could be collected at differing rates. Most years saw the rate of two shillings per hide, but in crises, it could be increased to as much as six shillings per hide. Coinage between the various parts of his domains continued to be minted in different cycles and styles. English coins were generally of high silver content, with high artistic standards, and were required to be re-minted every three years. Norman coins had a much lower silver content, were often of poor artistic quality, and were rarely re-minted. Also, in England, no other coinage was allowed, while on the continent other coinage was considered legal tender. Nor is there evidence that many English pennies were circulating in Normandy, which shows little attempt to integrate the monetary systems of England and Normandy.