As well as the information provided by secret901-ga in his comment,
here's some other facts on the "onion dome" architectural style...
"A peculiar feature of Russian Orthodox churches is the presence of
onion-shaped domes on top of the cupolas. In the early history of the
Russian Church, especially in Kiev, the first capital, the domes of
the churches followed the typical Byzantine rounded style, but later,
especially after the Mongol Period, Russian churches tended toward the
onion domes, which, in many places, became quite stylized. Historians
are not in agreement as to the origin of this particular style, but
some point to the possible influence of Persia on this peculiar
feature of Russian church architecture, while others argue that since
this style was more popular in the far North of Russia, it had a
practical application, in that the shape was particularly suited to
shed the large amounts of snow common in the region."
From "Orthodox Art and Architecture"
"In Russia the familiar "onion" dome was developed by the thirteenth
century, perhaps in response to weather conditions (it sheds snow
easily, preventing it from accumulating at the seam between the dome
and the drum)."
For further reading, this site has an excellent article on Orthodox
Architecture, well worth the read, in my opinion...
"The characteristic onion dome first appeared in Novgorod on the
Cathedral of Sancta Sophia, in the eleventh century."
From "Russian Architecture: The Golden Ring of Ancient Cities."
"For example, well known theory (sic) explains that the famous onion
shape of cupolas is the evolution of the flat Byzantine dome and the
Russian wooden gable."
A site with some excellent examples of onion dome architecture is "The
Empire That Was Russia" at
Links to a variety of Russian Orthodox Churchs displaying the onion
dome style can be reached at the "Glass, Steel, and Stone" site
And finally, there's an untrue, but cute, urban legend that Hershey's
Kisses were invented by a homesick Russian. :-)
Search strategy: "onion domes" architecture history; "onion domes"
church architecture history; "onion domes" Bohemia Czech