The history of Mexico in the second half of the sixteenth century and in the seventeenth as a whole is a vast and so far largely unpainted canvas. Any limited study, such as this one, while answering some questions, can hardly fail to raise others and to leave connections unmade or only badly made.

This study throws light on an episode in the northward expansion of New Spain. The power of wealth as a force in extending Spanish settlement into hostile regions is scarcely shown better anywhere than in the creation of the towns of the Zacatecas district. It appears, also, that this expansion into the lands of rich minerals was a prime cause of the development of the agricultural regions of the Bajío and Michoacán. Settlement and farming activities trailed in the wake of the silver rush. The city of Zacatecas was a great magnet in the north for much of the later part of the sixteenth century and the early years of the seventeenth, drawing roads, supplies and men to itself from central Mexico. And as, for many years, the effective northern terminal point of the Camino Real de la Tierra Adentro, Zacatecas was not only a destination in itself, but also a centre of distribution and trade for a wide area of the northern plateau, embracing New Biscay and New León, and ultimately, New Mexico. Up to the time of the Parral strike, in the early 1630s, this northern area was empty and unproductive of all but cattle.