Mosques in Moscow?

The first few buildings I saw in Moscow was these domed structures. And there were lots of these domed structure which looked like our mosques. But they are definitely not mosques. I was told that there are only 4 mosques in Russia for a city of about 12 million people but I only saw 2 (next posting). These other domed structures are the Russian Orthodox Christian Churches. I haven't had time to brush up on my architecture history as to why Russian churches resemble mosques (Russians called mosques mechet pronounced as mesyet which is very close to our pronunciation masjid). Perhaps someone can comment on this? I know there is an architect in my list of readers.