The outer curtain wall was started by King Henry II in the 1180s. The extent of the wall built during Henry’s reign is unknown but it was unfinished at his death in 1190. Although the outer defences of the Castle were incomplete there is no record of any substantial work at Dover until the reign of King John (1199-1216). Between 1205 and 1214 John spent over £1000 on Dover, the bulk of this was spent on continuing his father’s outer defences.In 1216 the outer defences were tested when the Castle was besieged by French forces under Prince Louis in an attempt to depose King John. The gate at the northern extremity of the outer defences was undermined by the French and collapsed. The Castle was held for the King by Hubert de Burgh, who with his heroic defenders was able to plug the breach with timber baulks. In this way they continued to hold out until the death of King John, and the accession of his infant son Henry III, occasioned the withdrawal of Prince Louis and his forces.The siege had exposed the weaknesses of Dover’s defences and it was to be the business of Hubert de Burgh and the new King’s government to make it good. Between 1217 and 1256 some £7500 was spent on the castle. The damaged gateway was rebuilt, not as a gateway but as a massive triple tower to strengthen this vulnerable point. The great outer curtain wall was completed and a new gateway, the Constable’s Gate was built to replace the now blocked northern entrance.The towers of the outer curtain wall once made a far more splendid sight than they do today, towering over the wall itself. In the eighteenth century the towers were reduced to their present height to make bases for the new artillery.