The first two rulers to make use of siege engines to a large extent were Philip II of Macedonia and Alexander the Great. Their large engines spurred an evolution that led to impressive machines, like the Demetrius Poliorcetes' "Helepolis" (or "Taker of Cities") of 304 BC: nine stories high and plated with iron, it stood tall and wide, weighing . The most used engines were simple battering rams, or "tortoises", propelled in several ingenious ways that allowed the attackers to reach the walls or ditches with a certain degree of safety. For sea sieges or battles, seesaw-like machines ("sambykē" or "sambuca") were used. These were giant ladders, hinged and mounted on a base mechanism and used for transferring marines onto the sea walls of coastal towns. They were normally mounted on two or more ships tied together and some sambykē included shields at the top to protect the climbers from arrows. Other hinged engines were used to catch enemy equipment or even opposing soldiers with opposable appendices which are probably ancestors to the Roman corvus. Other weapons dropped heavy weights on opposing soldiers.