Currently, men and women participate in six events. These are the single, double, and quadruple sculls, as well as the lightweight double scull, eight, and coxless pair. Men also compete in two more events: coxless fours and lightweight coxless fours. Women can enter up to five events. The exceptions are the heavyweight rowing events, which are only for men, and the mixed double sculls, which are an open event for both men and women. In ancient Greece, there were only three types of boat used for naval warfare: the coracle, the trireme, and the rowing ship. The coracle was a small, round boat with no more than 1 or 2 meters (3-6 feet) of depth. It was used by warriors on land or sailors at sea. The trireme was a larger version of the coracle that was used for battle by soldiers from different cities who wanted to avoid fighting each other directly. They would instead hire champions from each city to fight for them. Finally, the rowing ship was the largest type of boat used by Greek and Roman navies. It was usually made out of wood and had up to 70 oars per side. Rowers sat facing forward, one behind the other, using their legs to power the boat along the river or ocean. There were two types of rowing ships: those that were sailed by slaves and those that were not.