Are we sure about beacon tower in every city?

I have two cities 2 miles apart, and a beacon tower in only one of them. I was alerted about both attacks on the city without the beacon tower AND attacks on the valleys of the city without a beacon tower.

Unless being very close to each other matters, I think only one beacon tower is needed.

Also, lvl 2 forge can be destroyed after getting workshop lvl 1 (required for walls).

You need a stable lvl 1 for EVERY upgrade of the relief station.