While keeping in focus Kautilya's Arthashastra, examine the fort architecture of ancient India. What major changes occurred in the same after advent of Muslim conquerors? Examine.

Arthashastra has listed the following types of forts:

• Jala-durga(Water fort)
• Antardvipa-durga(island fortress): surrounded by natural (sea or river) water bodies.
• Sthala-durga(plain fortress): surrounded by artificial moats or irrigated by a river.
• Giri-durga(Hill fort)
• 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.
• Mahi-durga(Earthen fort)
• Nri-durga(Human fort) This is defended by a large number of loyal and experienced warriors.

When the Muslims invaded, there was a change in the style of construction of forts. The Muslims introduced the idea of construction of a citadel in the centre and putting in more area between the citadel and the walls. Example can be cited of Golkonda and the Berar fort. Further, gates of medieval Indian forts were highly decorated. The walls of the forts were often looked higher from the outside than the inside as the forts made use of the natural rock formations on hills. The main gate to the forts was located mostly facing north direction, this was to avoid its deterioration by the rains, winds and the sun.