In 1822 Minas became a province of the empire created by Dom Pedro I., though a revolutionary outbreak had occurred in Ouro Preto the year before.
The city was built by the state on an open plateau, and provided with all necessary public buildings, gas, water and tramway services before the seat of government was transferred from Ouro Preto.
The circumstance that the gold turned black on exposure to the humid air (owing to the presence of silver) gave the name of Ouro Preto to the mountain spur and the settlement.
When the empire was overthrown in 1889 and Minas Geraes was reorganized as a republican state, it was decided to remove the capital to a more favourable site and Bello Horizonte was chosen, but Ouro Preto remained the capital until 1898, when the new town (also called Cidade de Minas) became the seat of government.
With the decay of her mining industries, Ouro Preto had become merely the political centre of the state.