Complex sentence: A Censorship Board was organized, headed by Prince Alexander Kurakin, and in the last years of the eighteenth century, 639 books were confiscated in the Russian Empire, most of them--552 volume--at the Riga customs office.
Split into simpler sentences: A Censorship Board was organized, headed by Prince Alexander Kurakin. In the last years of the eighteenth century, 639 books were confiscated in the Russian Empire, most of them--552 volumes--at the Riga customs office.