Concerning the historical significance of Tughlaqabad Fort, examine the following statements:

1. It was one of the earliest examples of Indo-Islamic military architecture in India.
2. Tughlaqabad Fort was part of a larger city plan envisioned by Ghiyas-ud-din Tughlaq.
3. The fort maintained its strategic importance throughout the Mughal era.
4. The fort was designed to protect the capital of the Tughlaq dynasty from Mongol invasions.

Which of the statements given above are correct?