Caste system in ancient india: Did you mean...?

The Shushtar Hydraulic System is a Sasanian era (3rd century CE) water irrigation system in Shushtar in Iran that included watermills, dams, tunnels and canals. The mills, one of which is still functioning, were used to grind wheat and barley...

The entrance to the water system at Tel Gezer in central Israel. This photo was taken during the 2011 excavations of the water system by the New Orleans Baptist Theological Seminary. The water system is believed to have been built during...

A sepoy was an Indian soldier in the armies of various states and European trading companies in the Indian subcontinent and then, from the second half of the 19th century, in the British Indian Army. Recruited from many different population...

The life of wealthy Romans was filled with exotic luxuries such as cinnamon, myrrh, pepper, or silk acquired through long-distance international trade. Goods from the Far East arrived in Rome through two corridors – the Red Sea and the Persian...

The Portuguese Empire was established from the 15th century and eventually stretched from the Americas to Japan. Very often a string of coastal trading centres with defensive fortifications, there were larger territorial colonies like Brazil...

A map of the Inca road system which included some 40,000 km of routes.

The underground channel of a qanat in the Turfan water system in the Turpan Depression of Xinjiang, China.

Earth's solar system by NASA and Rawpixel.

An illustration of the solar system by Martin Kornmesser. From The International Astronomical Union.

A photograph of part of the tunnel network of the Maginot Line, the defensive system built along France's eastern frontiers prior to the Second World War (1939-45). From the Schoenenbourg fort, Bas-Rhin, France.