It must, however, be remarked that this success was only obtained by a complete change of policy on the part of the dukes. They no longer, like their mediaeval predecessors, opposed the development of the towns by oppressive measures. On the contrary, they did all in their power to protect and expand this prosperity, not only by securing peace and commercial liberty, but also by taking special measures in case of emergency. Philip the Good, on several occasions, attempted to arrest the decadence of Ypres caused by the development of the English cloth industry. In spite of the opposition of Ghent and Ypres, Charles the Bold undertook important works in order to dredge the estuary of the Zwyn, which was rapidly silting up, and thus to keep open, if possible, the port of Bruges. At the same time, the dukes encouraged the trade of Antwerp and gave the first impulse to the maritime activity of the ports of Holland. The Burgundian princes did not live isolated in their feudal castles; they made it a rule to reside in their large towns, either Ghent, Bruges or Brussels, where they held their courts and where they contributed, by their display of luxury, to the general prosperity. This solicitude for the welfare of the large towns was not altogether disinterested. The dukes realized that their power rested not so much on their military forces as on their wealth, and that their wealth depended on the riches of their towns. They understood, according to a contemporary historian (Chastellain), that "in the fullness of substance and money, not in dignities and highness of their rank, lay the glory and the power of princes."