Porto Velho (Old Port) is the capital of the Brazilian state of Rondônia, in the upper Amazon River basin. The population is estimated to be 435,732 people (IBGE/2010). Located on the border of Rondônia and the state of Amazonas, the town is an important trading center for cassiterite, the mining of which represents the most important economic activity in the region, as well as a transportation and communication center. It is located on the eastern shore of the Madeira River, one of the main tributaries of the Amazon River. It is also Rondônia's largest city, and the largest state capital of Brazil (by area).
The municipality occupies most of the border between Amazonas and Rondônia, and is simultaneously the westernmost and northernmost city in the state.