Short answers, pulled from the story.
Kievan Rus' converted to Orthodox Christianity in 988 AD under Vladimir the Great. According to legend, the beauty of the Hagia Sophia in Constantinople influenced the choice of Orthodoxy, and the conversion immediately set off a program of monumental ecclesiastical construction, initially carried out by imported Greek and Byzantine masters using the Byzantine inscribed cross plan.
The onion dome emerged in Novgorod, where the central dome of the Cathedral of St. Sophia was converted to the onion shape during the twelfth century. The form was most likely adopted for aesthetic reasons, though its distinctive shape also prevents snow from accumulating, an advantage in a northern climate.
Aristotele Fioravanti, a Bolognese architect born around 1420, oversaw the dismantling and rebuilding of the Kremlin's Dormition Cathedral after arriving in Moscow in 1475. He introduced Italian Renaissance geometric rationalism and founded a brickworks that produced stronger bricks than those previously used in the city.
Peter the Great founded Saint Petersburg in 1703 as Russia's new capital. Its three radiating streets were based on the layout of Versailles, and its tree-bordered canals were inspired by those in Amsterdam. Peter forbade masonry construction elsewhere in Russia in 1714 to concentrate labour and materials on the new city.
The Monument to the Third International, planned in 1919 by Vladimir Tatlin, was a proposed 400-meter spiral structure wound around a tilted central axis with rotating glass chambers. It was deemed impossible to construct at the time but inspired a generation of Constructivist architects in Russia and abroad.
In 1955, Nikita Khrushchev called for removing decorative extras from buildings and developing mass-production technology to speed up housing construction. Prefabricated concrete blocks, precut for doors and windows, were produced in specialized plants and assembled on steel frames in standardized series such as the II-32. The five-story Pyatietazhki block became the dominant housing form of the period.