The development of the baronial castles in England were affected by the economic changes during the period. During the 13th and 14th centuries the average incomes of the English barons increased but wealth became concentrated in the hands of a smaller number of individuals, with a greater discrepancy in incomes. At the same time the costs of maintaining and staffing a modern castle were increasing. The result was that although there were around 400 castles in England in 1216, the number of castles continued to diminish over the coming years; even the wealthier barons were inclined to let some castles slide into disuse and to focus their resources on the remaining stock. The castle-guard system faded into abeyance in England, being replaced by financial rents, although it continued in the Welsh Marches well into the 13th century and saw some limited use during Edward I's occupation of Scotland in the early 14th century.