PETRIOU (also called Cha-chang-sao)  , a town and port of Siam, in the division of Pachim, about 45 M . E. of Bangkok . It is the centre of that part of southern Siam which is watered by the Bang Pakong River . It is built on low-lying, swampy ground, about ro m. from the mouth of the above river . The population is about io,000, mixed Siamese and Chinese, the latter slightly predominating . Rice-mills give employment to a large number of indentured Chinese coolies, but the inhabitants are chiefly engaged in agriculture . A railway connecting with Bangkok was opened in the spring of 1908 .