conquest of the Aztec empire, Hernán Cortés realized the importance of the Chapultepec aqueduct to the Aztecs and cut the water supply to Tenochtitlan. In the colonial period, the Chapultepec aqueduct continued to function, with 904 arches and an open air path for drinking water. In the late nineteenth century, there were major public hydraulic works undertaken to create a network of piped fresh water to Mexico City, since scientific ideas had identified water as a vector for disease. Shortly after the Spanish conquest, the aqueduct of Acámbaro was constructed in Guanajuato. The Zacatecas aqueduct was constructed to supply drinking water to the major mining center. A Roman-style aqueduct of Queretaro was completed in 1738 to provide drinking water to the provincial capital of Querétaro. It was privately funded by Don Juan Antonio de Urrutia y Arana, Marques de la Villa del Villar del Aguila. It functioned into the twentieth century to supply drinking water to the city and continues to supply water to the city's water fountains. Other colonial-era aqueducts are the Morelia aqueduct; the Saucillo aqueduct in Huichapan, Hidalgo state; the Chihuahua aqueduct; the Guadalupe aqueduct in the Villa de Guadalupe, in northern Mexico City; another constructed near the capital was the Santa Fe aqueduct; and also the Tepozotlan aqueduct. Although many aqueducts were built in the colonial era, there have been no studies of their impact on their local watersheds. Agriculture and ranching Much of the environmental literature on the post-1492 expansion of agriculture and ranching of cattle and sheep falls into the category of environmental degradation or destruction, what environmental scholars call “declension.” An early study of the introduction of sheep into Mexico found that the environmental impact of sheep grazing in colonial Mexico is the subject of a study of the Mezquital Valley, which went from a thriving area of traditional peasant agriculture to one devoted sheep grazing. Sheep were one of the animals introduced to Spanish America with important consequences for the environment. Since sheep graze vegetation to the ground, plants often do not grow back. Wool was a major economic resource for the domestic cloth market in Mexico, so sheep ranching expanded during the colonial era, in many cases leaving ecological destruction. Antedating Melville's study on a particular place in colonial Mexico is a study by the transfer of cattle and sheep to New Spain, as well as a subsequent study. Research by