The development of medieval fortifications depended on the speed of progress and innovation of the attacking military force. From the disintegration of the Roman Empire and use of abandoned forts and fortified cities to the new stone fortifications with numerous advances, improvements and innovations. This balance of power was a major feature of siege warfare in the Middle Ages and was repeatedly disturbed by the invention of the trebuche and cannon. Economic, political, religious and other factors marked the appearance of the Middle Ages and, accordingly, medieval warfare. The First Crusade provides excellent examples how much balance of power depends on a smallest things and one single siege tower has changed the outcome of the war. The decline of the king's power and the transfer of the right to build fortifications to his subjects led to the construction of new fortifications, but at the same time weakened the king's absolute power.