SEE THE WORLD'S GREATEST ENGINEERING MARVELS

THE COLOSSEUM



Rome's Colosseum was commissioned by the Emperor Vespasian in AD 72 on the marshy site of a lake. Here deadly gladiatorial combats and wild animals fights were staged free charge for public viewing. While practical in design, with 80 arched entrances to allow easy access for an estimated 55,000 spectators, the Colosseum is also a building of great classical beauty.

HAGIA SOPHIA 



The 'Church of the Holy Wisdom', Hagia Sophia is among the world's greatest architectural achievements. More than 1400 years old, it stands as a testament to the sophistication of 6th-century Constantinople, and had a huge influence on architecture in later centuries. In the 15th-century, the Ottomans converted it into a mosque: the minarets, tombo and fountains date from this period.

THE GREAT PYRAMID



Pharaoh Khufu's pyramid, commonly called the Great Pyramid of Giza, was built using only simple surveying tools but with such remarkable precision that the greatest difference in the length between its four 230-meter-high sides is just five centimeters. The pyramid is estimated to contain more than two million stone blocks weighing on average 2.5 tonnes, with some weighing up to 15 tonnes. Although the construction methods and purpose of some of its chambers are unknown, the architectural achievements is clear.

GREAT WALL OF CHINA



The Great Wall once snaked across Chinese landscape, over deserts, hills and plains, for more than 8851 kilometers. Yet, despite its seemingly impregnable battlements, the wall was ultimately an ineffective barricade. In the 13th-century it was breached by the ferocious onslaught of the Mongols and then in the 17th-century by the Manchu. Today, its dilapidated remains crumble across the rugged terrain of northern China and only selected station have been restored.

MACHU PICCHU



The 'Lost City of the Inca' in one of the most spectacular archaeological sites in the world. Perched high on the saddle between two peaks and often shrouded in cloud, it is almost invisible from below. A site of just 20 square kilometers, it was built in 1460 by the Incan ruler Pachacuti Inca Yupanqui as a royal retreat. About 1000 people inhabited the area and they were self-sufficient, being surrounded by agricultural terraces and watered by springs.