What's the "eye" symbol on the map about?

[Dude]

If you zoom out you can see an eye symbol that has lashes above and below. If you zoom back in you see a roundish structure that looks like a temple or some such. Hovering with the mouse over that tile doesn't show anything special. It's not a ruin. What is the significance of it?

[Nemo, Forevermore]

they are foundations that you use to build watchtowers starting in tech era II

[Dude]

Awesome, thanks!