The Nedumkotta was built primarily to resist the invasion under Hyder Ali Khan against Travancore State and southern parts Cochin state.. It was raised mainly with clay and mud, and reinforced with stones, laterite and granite at strategic places. It started from the KrishanKotta on the west coast, above Kodungallur, and stretched up to the Anamala Hills on the Western Ghats. It was about 48 km long, 20 feet wide and 12 feet high. Its alignment was along the Periyar river on the west coast up to Chalakudy from where it went along the Chalakudy river up to the Annamalai Hills in the east. There were underground cells to store gunpowder and other war materials, special chambers for soldiers to live, and look-outs and mounted field-guns all along the fortification. Besides, on the north side of the fortification, ditches were dug twenty feet wide and sixteen feet deep, and filled with thorny plants, poisonous snakes, and hidden weapons. On the south side as well as on the top of the fortification, wide roads were laid for the convenience of military movements.