1) The greatest empire does not simply mean size, although that is a key requirment... Overall the Romans were the greatest, they changed the world forever. 
 
2) Then equal second would most likely be the Spanish and Ottoman Empire. Both had always been in competition with each other, and both kept a balance in the world for a time.. Islam in the east, and Christianity in the west. The Spanish defeated the Ottomans on many occasions, but the Ottomans outlived the Spanish, therefore it is too hard to decide a better of the two.
 
The Spanish Armada was defeated, but in the end the Spanish forced the British to surrender and sign a treaty. Spain defeated pretty much everyone at least once in Europe and America... They destroyed the Ottoman fleet at the battle of Lepanto with their invincible "tericos" infantry.
 
The Ottomans subjagated all the Arabs, conqured the balkans and destroyed the Byzantine Empire.. Hell, they even came close to conquering Austria, and defeated the Russians many times.
 
3) British Empire... Hard to imagine they accomplished what they did in the time they did.
 
4) Byzantine Empire. I know at one time they were the eastern Roman empire, but they were autonomous from Rome, and lasted more than one thousand years after the Barbarians destroyed Rome. These people accomplished much, and their wealth, time of existence, and power was great.
 
5) Mongols: Strength and land... but didnt last all that long compared to the major empires and their legacy was really non-existent. THe mongols did achieve massive amounts of land however.
 
6) Persian Empire: Long lasting greatness and one hell of a legacy... Ironically if the Persians and Byzantines had not been at war all the time, and weakened each other so severely, Islam would not have been able to spread.
			
			2) Then equal second would most likely be the Spanish and Ottoman Empire. Both had always been in competition with each other, and both kept a balance in the world for a time.. Islam in the east, and Christianity in the west. The Spanish defeated the Ottomans on many occasions, but the Ottomans outlived the Spanish, therefore it is too hard to decide a better of the two.
The Spanish Armada was defeated, but in the end the Spanish forced the British to surrender and sign a treaty. Spain defeated pretty much everyone at least once in Europe and America... They destroyed the Ottoman fleet at the battle of Lepanto with their invincible "tericos" infantry.
The Ottomans subjagated all the Arabs, conqured the balkans and destroyed the Byzantine Empire.. Hell, they even came close to conquering Austria, and defeated the Russians many times.
3) British Empire... Hard to imagine they accomplished what they did in the time they did.
4) Byzantine Empire. I know at one time they were the eastern Roman empire, but they were autonomous from Rome, and lasted more than one thousand years after the Barbarians destroyed Rome. These people accomplished much, and their wealth, time of existence, and power was great.
5) Mongols: Strength and land... but didnt last all that long compared to the major empires and their legacy was really non-existent. THe mongols did achieve massive amounts of land however.
6) Persian Empire: Long lasting greatness and one hell of a legacy... Ironically if the Persians and Byzantines had not been at war all the time, and weakened each other so severely, Islam would not have been able to spread.
 
			 
 
		 
 
		 
 
		 
 
		