Although as a rule external appearance is an unsatisfactory criterion of age, still, other things equal, a large amount and good height of standing wall may be taken to indicate in a general way a more recent period of occupancy than wall lines much obliterated and merged into the surrounding ground level. The character of the site occupied is, however, a very good criterion of age. It was a rule of the ancient pueblo builder, a rule still adhered to with a certain degree of persistence, that enlargement of a village for the purpose of obtaining more space must be by the addition of rooms to those already built, and not by the construction of detached rooms. So well was this rule observed that attached rooms were often built on sites not at all adapted to them, when much better sites were available but a short distance away; and, although detached rooms were built in certain cases, there was always a strong reason for such exceptions to the general rule. At a late period in the history of the Pueblos this rule was not so much adhered to as before, and detached houses were often built at such points as the fancy or convenience of the builder might dictate. As the traditions are broken down the tendency to depart from the old rule becomes more decided, and at the present day several of the older Pueblo villages are being gradually abandoned for the more convenient detached dwellings, while nearly all of them have suffered more or less from this cause. The tendency to cluster rooms in one large compact group was undoubtedly due primarily to hostile pressure from outside, and as this pressure decreased the inherent inconveniences of the plan would assert themselves and the rule would be less and less closely adhered to. It therefore follows that, in the absence of other sufficient cause, the presence of detached rooms or small clusters may be taken in a general way to indicate a more recent occupancy than a ground plan of a compact, closely built village.