Khmelnytsky Uprising
The Khmelnytsky Uprising was known to Jews as "Gezeiras Tach VeTat", meaning the "Decree of [years] 408 and 409" (corresponding to 1648 and 1649). Some historians estimate that between 100,000 and 500,000 Jews were slaughtered during the Khmelnytsky Uprising from 1648 to 1658. See the section Khmelnytsky Uprising: Jews for an outline of the discussion about the actual numbers of Jews killed by the Cossacks.