It is believed that the Baltic languages are among the most archaic of the currently remaining Indo-European languages, despite their late attestation. Although the various Baltic tribes were mentioned by ancient historians as early as 98 B.C., the first attestation of a Baltic language was about 1350, with the creation of the Elbing Prussian Vocabulary, a German to Prussian translation dictionary. Lithuanian was first attested in a hymnal translation in 1545; the first printed book in Lithuanian, a Catechism by Martynas Mažvydas was published in 1547 in Königsberg, Prussia . Latvian appeared in a hymnal in 1530 and in a printed Catechism in 1585. One reason for the late attestation is that the Baltic peoples resisted Christianization longer than any other Europeans, which delayed the introduction of writing and isolated their languages from outside influence. With the establishment of a German state in Prussia, and the eradication or flight of much of the Baltic Prussian population in the 13th century, the remaining Prussians began to be assimilated, and by the end of the 17th century, the Prussian language had become extinct. During the years of the Polish-Lithuanian Commonwealth , official documents were written in Polish, Ruthenian and Latin. After the Partitions of Commonwealth, most of the Baltic lands were under the rule of the Russian Empire, where the native languages or alphabets were sometimes prohibited from being written down or used publicly in a Russification effort .. In what time frame did Prussia's population assimilate?