Philip II of Macedon planned to invade Persia but was assassinated, leaving the invasion to his son Alexander. As a young but experienced commander, Alexander invaded Persia in 334 BC, defeating their army at the Battle of Granicus. He went on to conquer Egypt, building the Lighthouse of Alexandria, and defeated Darius III at Issus in 331 BC. Alexander continued conquering territory until reaching India, but his army refused to go further. Alexander died in 323 BC at age 33 after contracting a fever, without naming a successor for his vast empire.