Aristotle and Alexander: The man who codified Greek ideas about nature, and the man who spread them abroad

Greek philosophers were edging towards the radical idea that there were no gods who controlled the destiny of life on earth from some detached mountaintop. Rather, it was man himself who, thanks to his own brainpower, could decipher the laws of the universe to become master of all nature.

Supreme among such thinkers was Aristotle (384BCE-322BCE). The scope of his works was truly immense, covering everything from speculations on the nature of the human soul to the physics of the universe; from city politics and personal ethics to the history of plants and animals; and from public speaking and poetry to music, memory and logic.

Aristotle combined what he considered the best of what he had learnt from his teacher, Plato, and other Greek philosophers such as Thales, with everything he observed in the natural world. It led him to a single, profound conclusion: underneath all reality there was indeed a fundamental set of universal natural laws that explained everything to do with life, the universe and everything from human politics to the weather. To understand these rules of nature was to understand reality. The key was careful observation of the universe and its systems by good use of the human senses and then, by using human reason and intellect, to uncover the truth.

The question that Aristotle's scientific, rational view of the world provoked was this: in a mechanistic universe governed by rules, what place was there for old-fashioned, whimsical gods? His answer was simple. It was the rules of nature themselves that were the very essence of all that is divine in the universe: "For God is to us a law, impartial, admitting not to correction or change, and better I think and surer than those which are engraved upon tablets," he said.

Aristotle gave mankind the confidence to explore, discover and learn. But such insights would be useless hidden in the mind of one brilliant man, or stored in a rich patron's library. To fulfil their potential, these ideas needed a force to scatter them far and wide, giving as many human cultures as possible the chance to exert the power of human brains over nature's brawn.

As luck would have it, Aristotle's pupil, the young Prince Alexander of Macedon, was just the right man at just the right time. Quite possibly it was his great teacher's passion for the natural world that fired Alexander, impregnating him with a feverish determination to see everything in the world for himself, conquering whatever empires lay en route.

Alexander ascended to the throne of Macedonia in North Greece at the age of just 20, in 336BCE. For the next 13 years Alexander led an army of 42,000 Greek soldiers on an extraordinary military adventure across Persia, Egypt and even into India. On his way, he famously "undid" the impossible-to-untie Gordian knot by slashing it with his sword, and he routed the Persian Emperor Darius III at the Battle of Issus in 333BCE. He then marched down the Mediterranean coast, laying siege to the city of Tyre, which he eventually took after seven months, clearing the way towards Egypt, where, thanks to the decline of Persian power, he was welcomed as a liberator and pronounced Pharaoh in 332BCE. Here, Alexander founded the most famous of all the cities named after him, Alexandria, establishing it as the main sea port linking Egypt with Greece, the maritime axis of a new and increasingly powerful Hellenic empire.

Eighteen months later, Alexander left Egypt, marching back to Persia, where again he defeated Darius at the Battle of Gaugamela. This time the Persian king fled from the battlefield only to be murdered by his own troops in the mountains of Media. The way was now open for Alexander to conquer all Persia, first marching on Babylon, then Susa, the ancient Assyrian capital, and finally Persepolis, the magnificent royal home of the Persian kings.

With the death of Darius and the submission of Egypt and Persia, Alexander's military goals had been accomplished. But still the warrior in him could not be controlled. Having sent many of his Greek soldiers back home, he now paid mercenaries to fight for him in a new imperial army, and set off on a three-year campaign to subjugate Scythia and Afghanistan before reaching the River Indus in northern India.

Despite Alexander's determination to cross the sacred River Ganges and march into the heart of India, his men had reached their limit. Eventually Alexander and a company of soldiers made their way back to Persia across deserts and plains. On the afternoon of 10 June 323BCE, in the palace of Nebuchadnezzar II in Babylon, Alexander died, probably of malaria. He was one month short of his 33rd birthday.

Many historians have devoted their professional lives to the study of this man, yet no one really knows what drove him to try to conquer the world. Whatever his motivation, the result of his conquests caused the Greek language to become the lingua franca across the entire Middle East and Egypt. Thousands of Greek people, some soldiers, others merchants, artisans, scientists and philosophers, moved abroad, taking with them their experimental world views. Of the seven wonders of the ancient world, five were Greek constructions – each one an awesome monument to these people's confidence in mankind's power over the natural world.

Roman love for all things Greek was particularly focused around the personality and career of Alexander, who after his death became antiquity's greatest role model. Roman emperors came to regard Alexander as the epitome of leadership, strength and courage.