Here is the list of 6 greatest empires of all time in the world.
Persian Empire or Achaemenid Empire
Akkadians, Assyrians, Sumerians, Hitites, Bactrians, Scythians, Parthians, Medes, Elamites, Egyptians, Ethiopians… Before the Romans, there were the Persians. They basically unified the whole of Central Asia which consisted of a lot of different cultures, kingdoms, empires and tribes. It was the largest empire in ancient history.
At the height of its power (16th–17th century), the Ottoman Empire spanned three continents, controlling much of Southeastern Europe, Western Asia and North Africa. It contained 29 provinces and numerous vassal states.
The Umayyad Caliphate was the second of the four Islamic caliphates (systems of governance), established after the death of Mohammed. It was ruled by the Umayyad dynasty, whose name derives from Umayya ibn Abd Shams, the great-grandfather of the first Umayyad caliph.
The Roman Empire
At first they were ruled by divine kings, then they became a republic (perhaps their greatest period) before finally becoming an empire. How a group of farmers, who started off fending wolves to protect their livestock, eventually became the greatest empire in all history is the stuff of legends.
Byzantine Empire, or Eastern Roman Empire, was the Roman Empire during the Middle Ages, centered on the capital of Constantinople, and ruled by emperors in direct succession to the ancient Roman emperors. It was called the Roman Empire, and also Romania.
The British empire was known as the largest empire in history, as it covered more than 13,000,000 square miles, which is approximately a quarter of the Earth’s total land area, and controlled more than 500 million people – again a quarter of the world’s population. As a result, the legacy it imprinted on these conquered lands is tremendous in terms of political reform, cultural exchanges and way of life.