Introduction The "medieval economic revolution"l of Song China was in large part a spatial transformation, the shift of the center of gravity of Chinese civilization from the Yellow River valley to the Yangzi River basin. Beyond the great commercial towns clustered around the Yangzi delta, the surge in production, wealth, and numbers of people also propelled many Chinese to seek out and exploit the untapped resources of the more remote parts of South China. Economic opportunity created new incentives to tame a forbidding wilderness. The present study focuses on the process of settlement and economic exploitation of the southwestern frontier during the period of decisive and sustained colonization that began during the Tang-Song transition. The area chosen as the subject of this book-the southern frontier of Sichuan, especially the prefecture of Luzhou and its subordinate territories south of the Yangzi, known as Southern Lu-typified the process of frontier settlement unfolding during the Song period.2 Song Sichuan largely corresponded to the modern-day province, with the addition of the' upper Han River valley, now part of Shaanxi prov­ ince. Since antiquity Sichuan had been renowned for its starkly contrast­ ing landscapes: the Chengdu Plain, whose agricultural wealth inspired the epithet, "Heaven's Storehouse," and the formidable mountain ranges which encircled the Sichuan Basin and sealed it off from the larger Sinitic world and from the non-Han peoples to the south and west. In the Warring States period this territory was divided between two 2 Introduction kingdoms, Shu in the west (with its capital at Chengdu) and Ba in the east (with its capital at modern Chongqing, known during the Song as Yuzhou). The polarity, roughly following the contours of the ancient Shu and Ba kingdoms, between the rich, densely populated western part of Sichuan and the vast wilderness of the east persisted throughout much of the imperial era. The Song initially divided Sichuan into two admin­ istrative regions: the west, or Rivers, and the east, or Gorges. In 1001 these two administrative units were each further subdivided into two routes (lu): Chengdu and Zizhou in the west, Lizhou and Kuizhou in the east. Western Sichuan was popularly known as Shu or the Rivers region, while the east, corresponding to ancient Ba, retained the frontier charac­ ter signified by its designation as the Gorges region. The Song prefecture of Luzhou, surrounding the confluence of the Tuo and Yangzi Rivers at the southwestern edge of the basin, lay at the intersection of these two regions and shared features of both. The northern portion of the prefecture, conveniently situated along major waterways, was celebrated for its rich agricultural and mineral resources. By contrast, the area known as Southern Lu, extending southward from the Yangzi River, encompassed many indigenous non-Han tribes as well as scattered Han frontier villages. Although a formal part of the empire since the Qin unification in the third century B.C., Luzhou comprised a zone of contact between Han and native peoples down to the eight­ eenth century. The boundaries between Han and native continually advanced and receded; but the Song dynasty stands out as a period of vigorous Han expansion and settlement, culminating in the enduring political hegemony of the Han. This phase of frontier expansion coin­ cided with-and, indeed, was in large part produced by-the spatial and social transformations of the Song period. The case of Luzhou, there­ fore, allows examination of how these changes shaped frontier settle­ ment and regional integration, in Sichuan and in China as a whole. The frontier, after all, is a special type of region. With its new territories and hitherto unavailable resources, it provides valuable oppor­ tunities for an expanding society. At the same time, the fragile, elongated spatial relationship between the center and the frontier limits the scope of human activities. Moreover, a frontier implies a zone of contact between two (or more) separate societies, one indigenous, the other .