When Alexander the Great marched into India, he soon came up against something he had never seen in warfare before - war elephants. Alexander was so impressed by these animal tanks of ancient warfare that he began to incorporate them into his army.
After his death in 323 BC, his successors continued to utilize this valuable and effective weapon.
In the succession struggles following Alexander's death, Seleucus I, founder of the Seleucid dynasty in West Asia, negotiated with Chandragupta, the first Mauryan ruler over northern India. He traded land for war elephants and then used the elephants to crush his rival Antigonus at Ipsus in Asia Minor in 301 BC. Coins depicting elephants were struck to celebrate his victory.
The Seleucids continued to use war elephants and Seleucus's son Antiochus I (281-261 BC) used them in his famous 'elephant victory' over the Galatians around 272 BC.
The Hellenistic Greeks also invented the battle-castle which was placed on the back of the elephant. The Ptolemies also had war elephants, but used African elephants when the Seleucids refused to give them any more Indian elephants.
War elephants, however, were quite cumbersome and soldiers learnt to side-step them and stab their flanks or hamstring them. Their appearance in ancient warfare was dramatic, but not lasting.
