Geographically , Srirangapatna is a rocky island formed by Cauvery River.That made it significant from a military as well as religious point of view.
The religious history of Srirangapatna dates back to 9th century AD when the Gangas ( Ganga dynasty ) ruled this region from their capital at Talakkadu. They built the Sri Ranganathaswamy temple in this island and hence the name Srirangapatna.
Later when the region came under the power of Vijayanagara Empire, Srirangapatna was the base of the Vijayanagaras viceroys. This continued till the Vijayanagara empire weakened. In 1610 the ruler of Mysore Raja Wodeyar I captured Srirangapatna. The Wodayar king moved his capital (of Mysore) to Srirangapatna.
Later the capital of Mysore was moved out of Srirangapatna to the present day Mysore City.
During the rise of Hyder Ali, the general of Mysore king, Srirangapatna again came into prominence. Hyder Ali and his much famed son Tipu Sultan converted Srirangapatna into a fortified city. That continued for many decades as the power center of south India.
Between 1766 and 1799 four wars were fought between the English East India Company and the Mysore, known in history as the Mysore Wars.
The first two were decisive against the Company forces. In that third Mysore War, Tipu Sultan suffered greatly and in the treaty that ensued he had to relinquish a great part of his kingdom (Mysore) to the allied forces of East India Company. The fourth and that last of Mysore war saw the fall of Tipu.
The final battle , Siege of Seringapatam ,was fought in this island. After a long siege the fort of Srirangapatna was breached. Tipu Sultan was killed in the pitch battle that followed the siege. The English reinstalled the Wodeyars of Mysore as the ruler of Mysore.
After the fall of Tipu, Srirangapatna lost its significance as a capital. The English troops used it as a garrison for some times before moving it out to Bangalore.
Many remains of the period are popular tourist attractions.