The entrance was often the weakest part in a circuit of defences. To overcome this, the gatehouse was developed, allowing those inside the castle to control the flow of traffic. In earth and timber castles, the gateway was usually the first feature to be rebuilt in stone. The front of the gateway was a blind spot and to overcome this, projecting towers were added on each side of the gate in a style similar to that developed by the Romans. The gatehouse contained a series of defences to make a direct assault more difficult than battering down a simple gate. Typically, there were one or more portcullises – a wooden grille reinforced with metal to block a passage – and arrowslits to allow defenders to harry the enemy. The passage through the gatehouse was lengthened to increase the amount of time an assailant had to spend under fire in a confined space and unable to retaliate.