Onomastics
The Wanradt-Koell Catechism
Toponyms and Place Names
The dominant language spoken in the modern-day territory of Lithuania, changed according to the nationality of the rulers at the time, and where in the kingdom, duchy or commonwealth you resided.
With the crowning of King Mindaugas, the Grand Duchy of Lithuania began to form, and its’ administrative language was Ruthenian. Latin, German and Polish were also used to record laws and write documents, and it is not until the 16th century that the Lithuanian language was written down — a Southern Aukštaitijan translation of the Catechism.
With the union of the Kingdom of Poland and the Grand Duchy in 1569, the nobility spoke Polish and Latin as a second language, and Lithuanian and Ruthenian were spoken by the peasantry.
Onomastics
Lithuanian
The Martynas Mažvydas Catechism (1547)
Postilla of Wolfenbüttel (1573)
Jonas Bretk?nas’ Postilla (1591)
Postilla catholicka (1599)
Ruthenian
Polish
Latin
These pages are a part of the Slavic Interest Group, a volunteer-run project with the aim of putting together links to as much information about a particular areas’ history prior to 1600, we can find.
The project webpage describes it as:
The Slavic Knowledge/Slavianskoe Znan’stvo Project is intended to provide an easy means of gaining knowledge about the countries that SIG covers. Each page, while maintained by different people, is organized using similar subject categories to aid research.
This is the Baltic section, covering the modern-day states of Estonia, Latvia and Lithuania.

Map of the Modern-day Baltic States, from Wikipedia.
As these pages are divided into the modern territories, decisions about under which heading the various baltic tribes would be grouped, the maps from Virtual Livonia and Wikimedia were compared.
The Latvia pages will then also cover the Curonian, Latgalian, Livonian, Semigallian, and Selonian tribes.
The Lithuanian pages will cover the Galindian, Lithuanian, Prussian, Scalvian and Yotvingian tribes.
Estonia, in contrast, only the Estonians and the occasional Finn.
Archaeology
Viljandi Archaeological Investigations