STEVE ALLEN / SCIENCE PHOTO LIBRARY STEVE ALLEN / SCIENCE PHOTO LIBRARY
Kumbhalgarh fort. This fortress, located in Rajasthan, India, was built by Maharana Kumbha from 1445 to 1458. Its 36-kilometre-long perimeter wall (partly seen here) is thought to be the second-longest wall in the world, after the Great Wall of China.
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