Spire

Cost of the 1st level:

15050120CRP 1.8
Spire is necessary to exchange signals with colonies outside your home planet. Highest Spire's level determines how many objects that can be controlled:
+1 planet, temple or PPS per each 3 levels
+1 asteroid per each 3 levels
+1 satellite per level

The spire is also needed to send the fleet with any order. During the defense of your planet Spire act as the center of communication of the allies on low orbit. Each level allows you to support 2 players in defense.
Comparison by level
Lvl The number of allies in defense
1 2
2 4
3 6
4 8
5 10
6 12
7 14
8 16
9 18
10 20