In the 9th century, the Danes were well entrenched in England. To keep peace, a borderline was agreed between the Danish and Anglo-Saxon areas. The Danish territory was soon called the "danelaw." Some of the best Britannic trading centers were located within the danelaw. The city of York, situated on the trade route from North to South England, became one of the most important market centers of Northern Europe. The town even had its own mint. Edward, king of Wessex (899-924), would not accept the loss of such a lucrative territory, however. With the help of his sister Aethelflaed, the queen of Mercia, Edward overthrew part after part of the danelaw. Around 920, with the exception of the kingdom of York, the former danelaw belonged to the kingdom of Wessex again.