The Thais, most historians believe, began migrating from southern China in the early part of the Christian era. At first they formed a number of city-states in the northern part of what is present-day Thailand, in places like Chiang Saen, Chiang Rai and Chiang Mai, but these were never strong enough to exert much influence outside the immediate region. Gradually the Thais migrated further south to the broad and fertile central plains, and expanded their dominance over nearly the entire Indochina Peninsula. Contradictory as it may seem, however, recent archaeological discoveries around the northeast hamlet of Ban Chiang suggest that the world's oldest Bronze Age civilization was flourishing in Thailand some 5,000 years ago.