At the beginning of the period the population was widely scattered and most of the villages were small unit pueblos which have already been mentioned. The fact that the people lived in small scattered villages would in itself indicate that no danger threatened. Even more indicative of peaceful times is the fact that the kiva was located outside the village walls. The kiva, an underground room, was used primarily by the men. The only exit was a small hatchway in the roof and through this only one man could emerge at a time. If a raiding party had surprised a small village while the men were in the kiva during a ceremony or at night the results would have been tragic. Early in the Great Pueblo period the people began to change the location of the kiva. Soon, in most cases at least, the kiva was placed inside the village and was surrounded by the houses. No longer was the underground room a death trap in case of a surprise raid. At about the same time tall round towers came into use. Sometimes they were built at the outer walls of the pueblo but very often the tower was built beside the kiva and was connected with it by an underground tunnel. The round tower, which stood higher than the rest of the village, would have served admirably as a lookout tower and connecting it with the men’s room would seem a natural development. It has been suggested that the tower may have had some ceremonial use since it was connected with the kiva. More practical, however, is the idea that it was a watch tower which resulted from a defensive need. Or, if one wishes to avoid taking sides, perhaps it served both purposes. Whatever was affecting the people now seems to have caused life in small villages to be less desirable for as we move farther into the Great Pueblo period we see the pueblos increase in size. It is true that some small pueblos were still in use but one of the outstanding characteristics of the period was the concentration of the population in pueblos of great size. An excellent example of this concentration is to be seen in the great Montezuma Valley which lies to the north and west of the Mesa Verde. At an earlier date the Pueblo Indians who occupied this valley lived in many small villages. During the Great Pueblo period the people seem to have banded together to form large communities. A number of enormous pueblos were constructed and in many cases they were built around the springs which supplied water for the populace. In the Mesa Verde the trend was the same. At the beginning of the period the people lived in numerous small pueblos. After a time they began to band together and toward the end of the twelfth century large pueblos were being built on the mesa tops and in the broad, shallow drainages at the heads of canyons. In some cases several small pueblos were built close together while in other cases several small pueblos were clustered around one or more large ones.