Why do they have domes on top of the cathedrals?
The onion domes first appeared when Ivan the Terrible ruled. They got the idea from Russians from Muslim countries. Some believe that onion domes first appeared in Russian wooden architecture above tent-like churches. They were supposed to prevent snow from piling on the roof. Some onion domes represent people, One onion dome represents Jesus, but when there are three or five it is representing the Holy Trinity or Jesus and the Four Evangelists. The color of the domes represent things to like the green, blue and gold domes represent the Holy Trinity the Holy Spirit of God, and Jesus. Green domes also represent submission, and often appear on monasteries. The domes can be a single color or a combination of colors.