Forts of Bharata: Bharata is a land of forts. The 365 Savant/Palegars, 108 Rajas, 56 Maharajas and the 4 – 6 Chakravarthis that governed / ruled this land, built the forts which have withstood the rigours of nature for hundreds of years. Chanakya’s Arthashastra (the Bharathiya treatise on economy, monarchy and military strategy) describes six major types of forts differentiated by their major mode of defence.

1. Jala-Durga (Water fort) Surrounded by water on all sides either natural or man-made. E.g., Vellur Fort, Vellur Tamil Nadu. 
   
   1. Antardvipa-durga (island fortress): surrounded by natural (sea or river) water bodies.
   2. Sthala-durga (plain fortress): surrounded by artificial moats or irrigated by a river.
      
2. Dhanvana or Maru-durga (Desert Fort): Surrounded by an arid area of at least 5 yojanas (73 km). E.g., Jaisalmer fort, Jaisalmer Rajasthan.
   
3. Giri-durga (Hill fort) Fort built either on top of a hill or using the slopes of the hill or sometimes even enclosing the whole hill itself.
   
   A Hill fort are of the following sub-types: 
   • Giri-Prantara-durga: Located on a flat hill summit. E.g., medieval forts such as Chittoor, Gwalior and Ranthambore.
   • Giri-parshva-durga: The fortifications and civilian structures extend down to the hill slope (not just the summit). E.g., Chitradurga fort, Chitradurga, Karnataka.
     
   • Giri-Guha-durga: Located in a valley surrounded by hills on which the outposts and the signal towers are located. E.g., Surpur Fort, Surpur, Yadgiri district, Karnataka. 
     
4. Vana-durga (Forest fort): Surrounded by a dense forest over a distance of at least 4 koshas (14.6 km). A Vana-Durga has the following sub-types: 
   
   • Khanjana-durga, built on a fen (Wet-land) surrounded by thorny forests. E.g., Vana Durga, Surpur, Yadgiri district, Karnataka. 
   • Sthambha-durga, built in the forest among tall trees; lacks sufficient water sources.
5. Mahi-durga (Earthen fort) These types of forts are either built of earthen walls or built using earthen walls and stone or surrounded by wetlands.
   
   They are of the following sub-types:
   1. Mrid-durga: surrounded by earthen walls. E.g., Karachi Fort, Karachi Pakistan.
   2. 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.
   3. Panka-durga: Surrounded by Wetland (fens) or in some places they are surrounded by quicksand.
6. Nri-durga (Human fort): This type of forts are defended by a large army of loyal and experienced warriors. Usually forts that are built on flat lands or city fortresses, populated by a substantial garrison. E.g., Gulburga Fort, Gulburga, Karnataka. 
   

7. Saptha Mandala Durga: This fort can be any of the above types, but it will have seven concentric rings of fortifying walls surrounding the central core which would have royal, civilian and army structures forming a small self-sufficient town.
   

Each of these types had its own advantages and disadvantages. For example, according to the Manusmriti, the Vana Durga (forest fort) suffers from Vanara (monkey) attacks, the Mahi Durga (earthen forts) gets swarmed with rodents, the Jala Durga (water forts) will be plagued by diseases. The Manusmṛti considers the Giri Durga (Hill fort) to be the best defensive structure. Some other Shilpa Shastras texts consider Giri Durga (hill forts) to be the abode of Gods and hence considered as most auspicious. The Mahabharata describes the Nri durga (Human fort) as the most effective fortification, whereas some other scriptures consider a Giri Durga built in the form of Saptha Mandala Durga as the best, secure and the most auspicious. In the future blogs I will be detailing about them with examples from my visits.