Complex sentence: The monastery prospered in the 16th and 17th centuries being lavishly sponsored by the Tsars of Moscovy, but it declined dramatically in the 18th century to the point that there were only two Russian and two Bulgarian monks left by 1730.
Split into simpler sentences: The monastery prospered in the 16th and 17th centuries being lavishly sponsored by the Tsars of Moscovy. In the 18th century the monastery declined dramatically to the point that there were only two Russian and two Bulgarian monks left by 1730.