The Achaemenid Empire was founded by Cyrus the Great in the 6th century BCE; it was an ancient Persian empire that spanned three continents, encompassing parts of modern-day Iran, Turkey, Egypt, and beyond. As the largest empire of its time, the Achaemenids wield immense power and influence, fostering cultural exchange and administrative innovations that shaped history. The empire's relationship with Alexander the Great began when he ascended the Macedonian throne in 336 BCE and embarked on a campaign to conquer Persia. Alexander's military brilliance and ambition led him to defeat King Darius III, the last Achaemenid ruler, in a series of pivotal battles, such as Issus and Gaugamela. These victories enabled Alexander to dismantle the Achaemenid Empire, replacing it with the Macedonian Empire, which stretched from Greece to the Indus River. The fall of the Achaemenids under Alexander's conquest significantly impacted the political landscape of the ancient world. It marked the beginning of the Hellenistic period, during which Greek culture spread throughout the conquered territories.