Fort Cornelis measured in length by between and in breadth. Two hundred and eighty cannon were mounted on its walls and bastions. Its defenders were a mixed bag of Dutch, French and East Indies troops. Most of the locally raised East Indian troops were of doubtful loyalty and effectiveness, although there were some determined artillerymen from Celebes. The captured station at Weltevreeden proved an ideal base from which the British could lay siege to Fort Cornelis. On 14 August the British completed a trail through the forests and pepper plantations to allow them to bring up heavy guns and munitions, and opened siege works on the north side of the Fort. For several days, there were exchanges of fire between the fort and the British batteries, manned mainly by Royal Marines and sailors from HMS "Nisus".