Three major methods were used for the construction of ancient Indian forts. The first consisted of earthen ramparts. Often they were constructed of the sand which was dug out of the ditch surrounding the fort. The second of rubble with earth on the outside which was more sturdy. The third type of construction was with stone and masonry work. The last was the strongest. Often materials from demolished forts were reused in the building of new forts.[2]
By 4 BCE, fortified cities were common in India. The largest ones were between the city of Mathura (on the Yamuna river) and Magadha (on the Ganges). Another series of forts in the south, was on the Ujjain(on the Narmada)leading into the Deccan. These are inferred by the remains of fort walls and bastions seen on excavation at Rajagriha and at several sites in the Gangetic plain notably Kaushambi. At the latter site huge walls of burnt brick, which look like they have been battered. There does not seem to be any formal planning of these forts. [3]
There are few descriptions of these ancient structures. The most noted is the one by Megasthenes, an ambasaddor of Seleucus I Nicator to the court of Chandragupta Maurya. He describes Patliputra as being gaurded by a ditch with wooden walls. The fort had 570 towers and 54 gates with colonnaded halls decorated with gold and silver. One such hall has been excavated and is one of the oldest stone structures in India. [4]
Though most of the structures have been decayed and are lost, India's legacy of ancient forts is seen mostly in the shastras(ancient Indian treatises) and in the reliefs on stupas. [5] On some of the early relief work, the carvings indicate that ancient Indian forts has crenallations, embrasures and sloping walls. [6] The Arthashastra the Indian treatise on military strategy describes six major types of forts differentiated by their major mode of defense.
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Detail on stupa at Sanchi showing evidence of crenallations and