ENOne of the most important historic sources is the Lithuanian Register, whose original is kept in Moscow, with a copy on microfilm available in Vilnius. It contains transcripts of a wide variety of documents, including records of gentry and magnate families of the Grand Duchy of Lithuania; sales, leases and liens of landed property; agreements with Gdansk merchants about the grain trade; decisions relating to management of forested lands; transcripts of royal privileges granted and of wills and testaments; documents of foundations connected with Jesuit colleges. A fault of the Lithuanian Register, however, is that entries were made irregularly, which was confirmed by Grand Chancellor of Lithuania Lew Sapieha in one of his letters. An analysis of the materials of genealogical and economic character reveals many interesting details about the territorial expansion of the great magnate clans. It leads to the conclusion that one of the primary goals of magnates was the gaining of political and economic influence beyond their home territories. But connections created for this purpose did not always facilitate communication and understanding in the complex ethnic, religious and political fabric of the old Polish Commonwealth.