It's 756 ft long on each side, 450 ft high and is composed of 2,300,000 blocks of stone, each about 2 1/2 tons in weight. and the whole structure is perfectly oriented to the points of the compass. Even in the 19th century, it was the tallest building in the world and, at the age of 4,500 years, it is the only one of the famous "Seven Wonders of the Ancient World" that still stands. Even today it remains the most massive building on Earth. It is the Great Pyramid of Khufu, at Giza, Egypt.