♥ They had a food surplus, meaning that whoever was working on it, that they had enough extra food to feed people who worked on the megaliths. There was a bit of people so they did have a lot of extra food.
There are many things one can infer from these civilizations just by knowing that they were able to build such massive structures. One was that they had a running civilization which was able to provide for its citizens in adeqaute amount - this allowed them to be able to undertake such feats. Another thing is that we know they had the necessary knowledge to actually build such structures - this tells us that they were relatively advanced for their age and time. Another thing we can know from this is that they probably valued some sort of rituals and had people who were at a higher level in society who also commanded for these structures to be built.