In the mid-nineteenth century, Mexico lived under the solar energy regime. A combination of animal and muscle, water, and wood powered the vast majority of human activities, from growing food – itself the main energy source – to extracting, producing, and transporting goods. Only some factories in the flourishing textile industry and silver mines had adopted steam engines, the first to mechanize certain stages of manufacturing, the second to draw water from flooded mines. Steam engines, while few, allowed Mexico’s inhabitants for the first time ever to convert heat into work without a human body or an animal. This transitional moment was part of Mexico’s long, eventful energy and environmental history. This included the sixteenth-century demographic collapse of the indigenous population, the critical role of silver mining, and important developments in the first decades of independent life, especially the loss of energy-rich northern territories to the USA. Mid-nineteenth-century Mexico was born from this history.