In 1524, the fort was ready. It had been preceded by a rapid work in wood, inside which then worked in stone.
The top of the hill is also a bulwark, surrounded by a parapet. Inside, a vast cistern is opened to collect rainwater, with three mouths of one foot wide, and the remains of a loft and a chapel can still be seen. This was built in 1630 for use of the Portuguese forces, and worked until their retreat in 1728.
Chaul suffered a heavy siege in late 1570. Beyond the fort, convents, churches, and private houses had served as defensive structures, and almost everything was heavily destroyed. It became obvious then that it was essential to modernize the defenses by fortifying. Thus began the enclosure of the city that gave it the form-urbis that characterizes it.
The initial fort was no more than a small square rocket, with about two thousand five hundred square meters of surface and walls about four and a half meters thick, where turrets can still be seen in three of the corners, . It was implanted in the south-southeast end, near the trading post and the beach. It was not until the mid-1530s that a first Christian temple - Our Lady of the Sea, the first matrix - was erected outside the southeast corner of the fort. Successive up gradations have transformed it into a building of respectable size and architectural quality.
The fortification measures 2828 feet in length with an average width of 89 feet. The outer wall rises 5 feet 3 inches high, topped by 305 crenels. It is accessed by eleven doors - four exteriors and seven interiors. The area within the walls of the fortification is divided into three spaces by two lines of fortified walls.
Chaul at that time was the main trading post, naval station and arsenal of the Portuguese in this part of India. The port of Chaul maintained an active maritime trade linking the coast of Mozambique with that of China (bread, crockery, opium, indigo, coconut, cinnamon, pepper, cloves, cloths, gold, ivory, and coffee slaves), and annually organized Missionaries’ expeditions and was visited by important personalities of his time like Afonso de Albuquerque, Vasco da Gama, S. Francisco Xavier, Diogo do Couto and Luís de Camões.
As per the then description, Chaul Fort used to be as strong as any in the world. On the land side, the only side for which it could be assaulted, was protected by a moat, which could only be overtaken by a drawbridge. The main entrance was guarded by a bronze lion and the highest tower by a bronze eagle. It had capacity for 7000 men and horses.
In 1740, Chaul was ceded by treaty to the Maratha. The city was later abandoned, falling into ruins. At the moment the set is in advanced state of degradation, hidden under the tropical vegetation.