Answer : 4. "Ranthambore"
Explanation :

1. Ranthambore is a historical fort and national park located in Sawai Madhopur district of Rajasthan. This fort was built by the Chauhan Rajputs in the 10th century. This fort is famous for its natural beauty and historical importance.

2. Ranthambore Fort is a huge and strong fort. This fort is situated on a high hill. The walls of the fort are very thick and strong. There are many temples, palaces, and other buildings inside the fort.

3. Impressed by the strong natural security system of Ranthambore Fort, Abul Fazal wrote that “All other forts are naked, whereas this fort is armoured”.