Although protected by a small fort built near the shoreline in 1521, the city of Chaul was not fortified. Just as the threat of a siege became evident, the captain of the city, Dom Luís Freire de Andrade ordered the evacuation of women, children and elderly to Goa and barricades be set up in the main streets with artillery. In October, Dom Francisco de Mascarenhas arrived from Goa with 600 men and immediately ordered the digging of an extensive network of ditches, trenches, earthen walls and defensive works around the outer perimeter of the city, fortifying outer households into blockhouses and demolishing others to clear the line of fire for the artillery. In December 15, the vanguard of the army of Ahmadnagar, arrived under the command of an Ethiopian general, Faratecão , and clashed with the Portuguese, who repelled the attack. The Nizam arrived with the rest of his army on December 21. Through a spy, the Portuguese uncovered that the forces of the Nizam Ul-Mulk Shah of Ahmadnagar  might have risen up to 120,000 men, including many Turkic, Abyssian, Persian, Afghan and Mughal mercenaries, 38,000 horsemen and 370 war elephants, supported by 38 heavy bombards. It is likely not all were fighting men; according to António Pinto Pereira:
Question: How did the Portuguese know how big the army of the Nizam was?
Answer: Through a spy