At a point a little more than halfway down its course, the Menam Chao Phaya receives the waters of its only tributary, the Nam Sak, a good-sized stream which rises in the east of northern Siam and waters the most easterly part (the Pechabun valley) of that section of the country.
All these valleys, except Morrope and Chao, are watered by rivers which have their sources far in the recesses of the mountains, and which furnish an abundant supply in the season when irrigation is needed.
The whole course of the Menam Chao Phaya lies through a perfectly flat country.
In central Siam, after Bangkok and Ayuthia, places of importance on the Menam Chao Phaya are Pak-Nam at the river mouth, the seat of a governor, terminus of a railway and site of modern fortifications; Paklat, the seat of a governor, a town of Mohns, descendants of refugees from Pegu; Nontaburi, a few miles above Bangkok, the seat of a governor and possessing a large market; Pratoomtani, Angtong, Prom, Inburi, Chainat and Saraburi, all administrative centres; and Lopburi, the last capital before Ayuthia and the residence of kings during the Ayuthia period, a city of ruins now gradually reawakening as a centre of railway traffic. To the west of the Menam Chao Phaya lie Suphanburi and Ratburi, ancient cities, now government headquarters; Pechaburi (the Piply of early travellers), the terminus of the western railway; and Phrapatoom, with its huge pagoda on the site of the capital of Sri Wichaiya, a kingdom of 2000 years ago, and now a place of military, agricultural and other schools.
