Abstract - The aim of this work is to explain and reveal the mutual benefits of computational processing of a dead language and a contemporary language. The dead language considered is Old-Church Slavonic. We shall try to point out that processing of a dead language is important not only for a diachronic study of the language material, and that annotation is not the straightforward process that it may seem to be. We also describe briefly two frameworks for the processing of Old- Church Slavonic: DBT and STIN-O-SANCT.