Chittagong (ˈtʃɪtəɡɒŋ ), officially Chattogram (Sitang), (Coṭṭogram, ˈtʃɔʈːoɡram), is the second-largest city in Bangladesh after Dhaka and third largest city in Bengal region. It is the administrative seat of the eponymous division and district. It hosts the busiest seaport on the Bay of Bengal. The city is located on the banks of the Karnaphuli River between the Chittagong Hill Tracts and the Bay of Bengal. The Greater Chittagong Area had a population of more than 5.2 million in 2022. In 2020, the city area had a population of more than 3.9 million.
One of the world's oldest ports with a functional natural harbour for centuries, Chittagong appeared on ancient Greek and Roman maps, including on Ptolemy's world map. It was located on the southern branch of the Silk Road. In the 9th century, merchants from the Abbasid Caliphate established a trading post in Chittagong. The port fell to the Muslim conquest of Bengal during the 14th century. It was the site of a royal mint under the Delhi Sultanate, Bengal Sultanate and Mughal Empire. Between the 15th and 17th centuries, Chittagong was also a center of administrative, literary, commercial and maritime activities in Arakan, a narrow strip of land along the eastern coast of the Bay of Bengal which was under strong Bengali influence for 350 years. During the 16th century, the port became a Portuguese trading post and João de Barros described it as "the most famous and wealthy city of the Kingdom of Bengal". The Mughal Empire expelled the Portuguese and Arakanese in 1666.
Like the rest of Bengal British East India Company took control of the city in 1793. The Port of Chittagong was re-organized in 1887 and its busiest shipping links were with British Burma. In 1928, Chittagong was declared a "Major Port" of British India. During World War II, Chittagong was a base for Allied Forces engaged in the Burma Campaign. The port city began to expand and industrialize during the 1940s, particularly after the Partition of British India.