Archeology can still tell us little of the first human occupants of Siam. The earliest evidence of man's existence here is furnished by celts, uncovered in the Peninsula and on the eastern plateau, which are supposed to date from the later Neolithic period; geology, however, gives us no reason to conclude that the makers of these implements were not preceded by other races.
[Illustration: 1. The rivers fall from the northern plateaus to the central plain through narrow defiles.]
[Illustration: 2. Ancient wall at Chiengmai. The city walls are preserved as picturesque ruins.]
[Illustration: 1. An international incident was caused by the European alpinist who first scaled the monolith to plant his nation's flag upon it.]
[Illustration: 2. Boats must be pulled upstream through the rapids by ropes.]
[Illustration: 1. The valuable gum resin, Bengal kino, is yielded by the "mai kwao" (_Butea frondosa_).]
[Illustration: 2. Young rice plants are transplanted from a seedbed to the flooded fields.]
[Illustration: 1. At the end of the rains, fish may be captured from the roadsides.]
[Illustration: 2. Cows and water buffaloes are treated as family pets.]
Among the mountains of the Malay Peninsula exist to this day small groups of dwarf, black-skinned, kinky-haired people, different from all other races of the country but closely related to the natives of the Andaman Islands and the Negritos of the Philippines; it has been surmised that these Ngo (Semang) are the dwindling remnant of a once numerous population, successors to (and possibly descendants of) the Neolithic men.
Following the Ngo and sometime during the past few millennia, it is believed that there came successive waves of a people of Mongolian origin who, making their way down the rivers, drove the primitive Negritos into the hills and settled in their place. Now conveniently known as the Mon-Annam family, their descendants are the Mon (Peguans), the Cambodians, and the Annamese, as well as numerous semibarbarous lesser tribes which persist among the mountains of the subcontinent.
Probably between two and three thousand years ago and certainly after the arrival of the Mon-Annam immigrants, another great population wave, known as the Tibeto-Burman family, rolled southward over Indo-China but chiefly descended the valley of the Irrawaddy (where they have given rise to the modern Burmese), thus scarcely entering Siam at all. Only in comparatively recent times, driven from their former homes by political disturbances, have tribes of this stock (Yao, Meo, etc.) migrated into Thailand and the territories to the east, where they are constantly being joined by others of their blood brothers from farther north.