Maybe not one of he largest in ever but uncertainly one of the most imressive at its times.
The Dardanelles Gun, a siege gun dating from soon after the fall of Constantinople in 1453. It is cast in bronze and was made in two parts: the barrel which holds the shot and the chamber which holds the charge. The two parts screw together gas tight. Overall length is 5.2 m and it weighs 16.8 tonnes. It fires a stone ball of about 300 kg some 1600 m. The rate of fire was very slow - about 15 rounds per day. Currently in the Royal Armouries at Fort Nelson, Portsmouth, England. A phantastic masterpiece of medieval engineering and metal casting.
http://www.royalarmouries.org/visit-...gle-object/196