Tysiacha. In Kyivan Rus’ (9th–10th centuries) a tysiacha (‘thousand’) was a military unit, commanded by a trusted appointee of the prince called the tysiatskyi. Each large city with its adjoining territories constituted a tysiacha, subdivided into sotni (‘hundreds’). Eventually the tysiacha became the largest administrative-military unit; it corresponded to a land or territory and was governed by a prince's appointee.
[This article originally appeared in the Encyclopedia of Ukraine, vol. 5 (1993).]