Among the many ‘unions’ between the Roman Church and the various Eastern Churches, none, perhaps, has been more unknown than the Union of Suzdal, 1222–1252. How important this union really was, outside the ecclesiastical questions involved, will appear immediately upon reflexion that its span coincides with the Tartar conquest of Russia and the consolidation of Tartar power. All the more startling, therefore, is the neglect of this union by Russian and non-Russian historians.