After conquering the Achaemenid Empire, Alexander set out to take over the Punjab region of India. In the area between the Jelum (Hydaspes) and Chenab River, he encountered a prince named Porus in what would become known as the Battle of the Hydaspes.
Despite the Punjab force's numerical superiority, including 200 elephants, Alexander's troops flanked Porus' left side. The maneuver caused the elephants to panic, and Alexander's highly mobile cavalry proved too strong for the Punjab force.
Presumably impressed with Porus' military elegance and spirit, Alexander allowed him to retain his kingdom after the battle. Porus became an ally and subordinate ruler of Alexander, until sometime between 321 BCE and 315 BCE, when he was assassinted by Eudemus, one of Alexander's generals.
During his reign, Alexander had created one of the largest empires in the world, and created a new Hellenistic civilization by leaving Greek colonists in his conquered lands. As he continued his conquest of Asia, the Assassins realized that Alexander's success could not be caused by military prowess alone, suspecting that he held the Staff.
Thus, in June 323 BCE, the Babylonian Assassin Iltani infiltrated the palace of Nebuchadnezzar II, where she poisoned Alexander and retrived the Staff. On 13 June, Alexander died of the poisoning, and his empire soon began to crumble.