Mathematics Used by Indians North of Mexico

Problems about the Mathematics Used by Indians North of Mexico will illustrate the very nature of their mathematics and their knowledge. First, because there is no evident theory, there seem to be few "mathematical" questions available. However, there is much to reason upon. You may need to seek additional sources of information to resolve some of the problems.

Problems

1. Evaluate the variety of sacred numbers as an aspect of cultural diversity, but more importantly as an aspect of common origins.
2. The sacred numbers four and five seem to be related to directions (four) and fingers (five per hand). However, why should there have been four directions? Is there something natural about four?
3. The number thirteen seems to be the oddest of the sacred numbers. Conjecture its origin.
4. The earthen works were constructed with a remarkable accuracy. This implies that these indians had a very good method of producing a right angle. What do you think it might be?