it is not completely clear when and why onion domes became a typical feature of russian architecture. the curved onion style appeared outside of russia, both in the western world and in the orient at a later time. but still several theories exist that the russian onion shape was influenced by countries from the orient, like india and persia, with whom the russian population and culture through history has always been in cultural exchange. byzantine churches and architecture of kievan rus were characterized by broader, flatter domes without a special framework erected above the drum. in contrast to this ancient form, each drum of a russian church is surmounted by a special structure of metal or timber, which is lined with sheet iron or tiles, while the onion architecture is mostly very curved. russian architecture used the dome shape not only for churches but also for other buildings.