About 1070, some of the Hohokam left the valley. Evidently many of these emigrants went north to the plateau region east of present-day Flagstaff, to plant in the moisture-conserving ash-fall area created by the eruption of Sunset Crater in 1064. Shortly after these Hohokam departed, many of the Sinagua moved down from the hills into the middle of the Verde Valley. This occurred about 1125. They lived much as they had before, but with two important changes: they adopted the Hohokam idea of irrigation, and they began building surface houses of rock and mud—an idea acquired from still another group, the Pueblo Indians, farther north. These Sinagua were the people who built the stone pueblos we find in the valley today. At first they erected small settlements on well-drained ridges overlooking their farmlands. Occasionally, also, caves were utilized for dwellings; the first 3 or 4 rooms of Montezuma Castle were evidently built in the 1100’s. From 1125 to 1200, the settlement at Montezuma Well was increased by groups of these Sinagua Indians who had left their homes in the foothills to the north and east. It appears that they joined some of the remaining Hohokam, as several customs of the latter survived up to 1400. In this period the Sinagua also utilized caves near their fields, and built a small pueblo on the west rim of Montezuma Well. Limestone rock for their masonry was available on the rim of the Well, and river boulders for foundations were taken from the creek. Mud and clay, which they mixed for their mortar, were easily obtained along the creek. [Illustration: _Ancient irrigation ditch near Montezuma Well._] As the years passed, more land was put under cultivation and more ditches were constructed. To insure adequate care of their farmland, 1- and 2-room “farm” structures were built on the slopes above and along the course of the main ditch. From these, the occupants were able to view the fields while irrigating and also could divert the water from the ditch below them whenever necessary. At their peak, the people at Montezuma Well were farming about 60 acres, or possibly more, and their main ditch was about 1 mile long. [Illustration: _Cut-away model of Montezuma Castle._] The Sinagua of the Verde generally lived in small pueblos until about 1250, at which time the center of the valley appears to have undergone a “real estate boom.” The buildings increased in size, and many of them were converted into forts with defensive walls, parapets, peepholes, and sealed doorways. Since the pueblos on the north and east fringes of the valley were abandoned in the 1200’s, it is believed that the Sinagua of that area probably were the ones who moved in to increase the population and size of the central villages. This move to the center of the valley was probably caused by nearly a century of almost continuous drought which began about 1200 and culminated in an especially severe drought from 1276 to 1299.