These objects require literally TONS of rare resources to build: bear tooths, deer antlers, metals, high-exploration herbs and stuff. May be even certain types of gatherable curiosities.
Make it nearly impossible to build in a reasonable time for a small villages.
As a result - you get an object, that boosts your village activity in a certain way.
For example:
+10% crop raising speed
or
+5% chance of successful ore smelting
or
+10% quality of all crafted metal items
etc.
Effects are not stackable, so building several Monuments of the same kind in one place with overlapping effect radius won't make sense.
Monuments effect radius is average, so you can't cover all your village fields with one Monument.
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This would make villages much more valuable and interesting way of social organization.
Building a monument requires collaboration of gatherers, hunters, miners and farmers - in different proportions depending on the monument type.
This is also a good resource sink, so villages don't get overstuffed with valuable goods and always have the need for more.
Might even encourage village trading.
Also - this would give additional reasons for raids and wars - why building your own monument, if you can steal one from your neighbours?
