Answer :

When Attila the Hun saw the Walls of Constantinople then he crossed the Danube twice and plundered the Balkans, but was unable to capture Constantinople.

Attila the Hun, was the ruler of the Huns from 434 until his death in March 453. He was also the leader of a tribal empire that included the Huns, the Ostrogoths, the Alans, and the Bulgars, among others, in central and eastern Europe. He is also considered one of the most powerful military rulers in world history.

During his reign, he was one of the most feared enemies of the Western and Eastern Roman empires. He crossed the Danube twice and plundered the Balkans, but was unable to capture Constantinople.

Attila the Hun's unsuccessful campaign in Persia was followed in 441 by an invasion of the Eastern Roman Empire (Byzantine), the success of which encouraged Attila to invade the West.

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