The techniques of warfare were transformed during the 15th and 16th centuries by the use of gunpowder and by substantial progress in the effectiveness and destructive power of artillery. Consequently new methods of fortification were introduced, and following the outbreak of the English Civil War most towns and castles had to be re-fortified. The main communication routes followed the lines of the old Roman roads so control of these, and of the major cities, was important. However, the sites that saw most fortification were the two capitals, London for the Parliamentarians and Oxford for the Royalists.