adopted by the Persians. War elephants were sometimes deployed for fighting in ancient warfare. They were first used in India and later adopted by the Persians. War elephants were also used in the Battle of the Hydaspes River, and by Hannibal in the Second Punic War against the Romans. One of the most important military transactions of the ancient world was Chandragupta Maurya's gift of 500 elephants to Seleucus I Nicator. Naval warfare was often crucial to military success. Early navies used sailing ships without cannons; often the goal was to ram the enemy ships and cause them to sink. There was human oar power, often using slaves, built up to ramming speed. Galleys were used in the 3rd millennium BC by the Cretans. The Greeks later advanced these ships. In 1210 BC, the first recorded naval battle was fought between Suppiluliuma II, king of the Hittites, and Cyprus, which was defeated. In the Greco-Persian Wars, the navy became of increasing importance. Triremes were involved in more complicated sea-land operations. Themistocles helped to build up a stronger Greek navy, composed of 310 ships, and defeated the Persians at the Battle of Salamis, ending the Persian invasion of Greece. In the First Punic War, the war between Carthage and Rome started with an advantage to Carthage because of their naval experience. A Roman fleet was built in 261 BC, with the addition of the corvus that allowed Roman soldiers to board enemy ships. The bridge would prove effective at the Battle of Mylae, resulting in a Roman victory. The Vikings, in the 8th century AD, invented a ship propelled by oars with a dragon decorating the prow, hence called the Drakkar. The 12th century AD Song Dynasty invented ships with watertight bulkhead compartments while the 2nd century BC Han dynasty invented rudders and sculled oars for their warships. Fortifications are important in warfare. Early hill-forts were used to protect inhabitants in the Iron Age. They were primitive forts surrounded by ditches filled with water. Forts were then built out of mud bricks, stones, wood, and other available materials. Romans used rectangular fortresses built out of wood and stone. As long as there have been fortifications, there have been contraptions to break in, dating back to the times of Romans and earlier. Siege warfare is often necessary to capture forts. Middle-ages Some of the military unit types and technologies which were used