he River Cauvery provided a natural defence for Seringapatam in all but the dryest months of the year. Haidar had greatly strengthened the fortifications of the island, inviting the advice and services of French military officers for this purpose. To the north and east rose a triple defence of formidable bastions, ditches and cavaliers, while to the east and west, there lay a line of redoubts (since destroyed). Batteries were strategically situated on the ramparts, and powder magazines and an arsenal were constructed. These massive defences endured for some forty years, and the names 'Lally's Bastion' and 'French Rocks' survive today, as a reminder of Mysore's European allies.

Beatson, writing in 1799/1800, noted the improvements and additions to the fortifications made since 1792 and the Third Mysore War. He comments 'Perhaps no place of the same extent of fortification ever required so much labour in construction. The rampart, which is thick and strong, varies in height from twenty to thirty-five feet and upwards; the whole of the revetement, except the north-west bastion, is composed of granite, cut in large oblong pieces, laid in cement, transversely, in the walls. The ditches are excavated in solid rock; a stone glacis extends along the north face, more with a view of making the outer part of the ditch than of covering the wall. The western ditch has not been constructed with much less labour: it is formed by a strong mound, or wall, of considerable thickness, parallel to the rampart, and entirely built of stone…… To the north-west angle of the fort, an entire new bastion of European construction, with faces and flanks, had been added; and a new inner or second rampart, having a deep ditch, extending the whole length of the north face, was in some forwardness.'