Plants have these because root nodules<span> are formed when nitrogen fixing bacteria called "rhizobia" start to enter the cells of a host </span>plant<span>. Rhizobia normally live inside of the soil and they </span>can<span> exist without a host </span>plant<span>.</span>
The fact that the Mayans were building great buildings in their period of existence, is a proof that they had a very big political power in the region, and not just political, but also military, economic, cultural power.
Only civilizations that are strong, well organized, and political powerhouses, have been able to build such big structures, because they had the conditions and time for it. For building such big structures, lot of wealth is needed, also lot of workers, and great engineers. The Mayans had it all. They had great engineers, the labor force was provided in general by the slaves, or by the the tribes that they were ruling over, and from all the tributes paid to them by the people they ruled over, they had surplus of wealth, which meant that they can perform such activities without damaging the empire.
