This letter, addressed to Tsar Alexander I of Russia by Wilberforce, makes reference to the Tsar's "solemn and sacred" (1) engagement against the slave trade which was made at the Congress of Vienna in 1815, and renewed at Aix-la-Chapelle. Wilberforce reveals that the transatlantic trade was still operating under the flag of certain powers, despite its condemnation by the "tribunal of Europe" (41). He describes the effect upon Africa, the conditions on slave ships and the progress made so far in abolishing the trade. The letter calls on the Tsar, as a principal guarantor of the congressional treaties on the slave trade, to mediate in European debates on this issue.