By the 4th century BC, fortified cities were common in India, with the largest being between Mathura and Magadha. The most notable description is one by Megasthenes, who described Pataliputra as guarded by a ditch with wooden walls and 570 towers and 54 gates.

Ancient Indian forts, found in shastras and stupa reliefs, had crenellations, embrasures, and sloping walls. The Arthashastra, an Indian treatise on military strategy, identifies six major types of forts based on their defense modes: Jala-durga (water fort), Antardvipa-durga (island fortress), Sthala-durga (plain fortress), Dhanvana- or Maru-durga (Desert Fort), Giri-durga (Hill fort), Prantara-durga (flat hill summit), Giri-parshva-durga (fortifications and civilian structures extend down to the hill slope), Guha-durga (valley surrounded by hills), Vana-durga (forest fort), Khanjana-durga (built on a fen surrounded by thorny forests), Sthambha-durga (built in the forest among tall trees), Mahi-durga (earthen fort), Parigha-durga (surrounded by earthen walls), Panka-durga (surrounded by fens or quicksand).

The term "fort" became common in India in the 17th-19th century, with local languages adding fort names to local words. British forts used simple designs at first. Many were privately owned. Three major methods of building were used: earthen ramparts, rubble with earth on the outside, or stone and masonry work, which were the strongest. Earthen ramparts allowed for higher and steeper walls, but the earthen core could accumulate water, requiring drainage channels. The third method involved using mortar, which was strong and long-lasting. In medieval India, burying humans in fort walls was believed to keep evil spirits away. The Sri Qila in Delhi buried 8,000 Mughal skulls, and Purandar Fort had a first-born son and wife buried in the foundation. Other fortifications included rock cut water cisterns, ponds, wells, and lakes. Parapets with merlons and loopholes were unique in Indian fortifications. The merlons were semicircular and pointed at the top. Loopholes were made in both merlons and crenels, either looking forward or downward. The shape of loopholes and merlons varied across the castle.

Muslim forts featured a citadel in the center and more space between the citadel and walls. Gates were highly decorated, with two distinct styles: Hindu with a lintel and Mughal with an arch. Forts used natural rock formations for defense against attacks, and the main gate was mostly facing north.

The British established trading posts along the coast to provide security against local rajas and European rival nations. Forts like Mumbai, Fort William, and Fort St George were built. They were simple due to the East India Company's refusal to pay more and the lack of trained engineers. However, hostilities with the French and the Company's growing power led to more complex designs. Many Indian forts were abandoned due to rulers' ambitions and have deteriorated over time, with some remaining private property.

North India:*

1. Red Fort (Delhi)

2. Agra Fort (Uttar Pradesh)

3. Fatehpur Sikri Fort (Uttar Pradesh)

4. Amber Fort (Jaipur, Rajasthan)

5. Jaisalmer Fort (Rajasthan)

6. Mehrangarh Fort (Jodhpur, Rajasthan)

7. Chittorgarh Fort (Rajasthan)

8. Kumbhalgarh Fort (Rajasthan)

9. Hari Parbat Fort (Srinagar, Jammu & Kashmir)

*South India:*

1. Golconda Fort (Hyderabad, Telangana)

2. Bekal Fort (Kerala)

3. Fort Kochi (Kerala)

4. Bangalore Fort (Karnataka)

5. Tipu Sultan's Summer Palace (Bangalore, Karnataka)

6. Vellore Fort (Tamil Nadu)

7. Gingee Fort (Tamil Nadu)

8. Thanjavur Maratha Palace (Tamil Nadu)

*East India:*

1. Fort William (Kolkata, West Bengal)

2. Barabati Fort (Odisha)

3. Raj Bari (Tripura)

4. Neemrana Fort (Rajasthan, near Delhi)

*West India:*

1. Gateway of India (Mumbai, Maharashtra)

2. Raigad Fort (Maharashtra)

3. Sinhagad Fort (Pune, Maharashtra)

4. Daulatabad Fort (Maharashtra)

5. Junagarh Fort (Gujarat)

6. Diu Fort (Diu, Union Territory)

Island Forts

1. Fort St. George (Andaman & Nicobar Islands)

2. Ross Island (Andaman & Nicobar Islands)

Some notable features and architectural styles found in Indian forts include:

- Mughal architecture

- Rajput architecture

- Dravidian architecture

- Islamic calligraphy and ornamentation

- Hindu and Buddhist influences

- Moats, bastions, and defensive walls

- Palaces, temples, and mosques within fort complexes