In 1748 he went to the court of the Ukrainian hetman Kirill Razumovsky, Aleksey's brother, to design the residences and churches in Baturin, Glukhov, and Koselets.
The region received its name after the Severians, an East Slavic tribe which inhabited the territory in the late 1st millennium A.D. Their main settlements included the present-day cities of Novhorod-Siverskyi, Chernihiv (Chernigov), Putyvl (Putivl), Hlukhiv (Glukhov), Liubech, Kursk, Rylsk, Starodub, Trubchevsk, Sevsk, Bryansk, and Belgorod.