Types of Ancient Indian Forts

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.

On some of the early relief work, the carvings indicate that ancient  Indian forts has crenellations, embrasures and sloping walls.

The Arthashastra the Indian treatise on military strategy describes six major types of forts differentiated by their major mode of defense:

• Jala-durga Water fort
• Antardvipa-durga island fortress: surrounded by natural sea or river)water bodies. E.g. Murud-Janjira.
• Sthala-durga plain fortress: surrounded by artificial moats or irrigated by a river.egDeeg Fort, Lohagarh Fort
• Dhanvana- or Maru-durga (Desert Fort): Surrounded by an arid area of at least 5 yojanas.
• Giri-durga Hill fort
• Prantara-durga: Located on a flat hill summit. E.g. medieval forts such as Chittor, Gwalior and Ranthambore.
• Giri-parshva-durga: The fortifications and civilian structures extend down to the hill slope not just the summit.
• Guha-durga: Located in a valley surrounded by hills, where the outposts and the signal towers are located.
• Vana-durga Forest fort: Surrounded by a dense forest over a distance of at least 4 kroshas.
• Khanjana-durga, built on a fen surrounded by thorny forests.
• Sthambha-durga, built in the forest among tall trees; lacks sufficient water sources.
• Mahi-durga Earthen fort Mrid-durga: surrounded by earthen walls
• Parigha-durga: Surrounded by earthen walls, as well as stone or brick walls. The walls are at least 5.4 m high and their width is half of their height.
• Panka-durga: Surrounded by fens or quicksand
• Nri-durga Human fort
• Defended by a large number of loyal and experienced warriors. Usually a city fortress, populated by a substantial garrison.

Each of these types had its own advantages and disadvantages. For example, according to the Manusmṛti, the forest fort suffers from monkey attacks, the earthen forts get swarmed with rodents, the water forts were plagued by diseases etc.

The Manusmṛti considers the Hill fort to be the best defensive structure. Some Sanskrit text consider hill forts to be the abode of gods and hence auspicious. The Mahabharata describes the Human fort as the most effective fortification.