Complex sentence: His main work was "De admiranda sacra et civili magnitudine Coloniae"... published in 1645, and today this is the only source of information on some events because a lot of documents have already been lost.
Split into simpler sentences: His main work was "De admiranda sacra et civili magnitudine Coloniae"... published in 1645. Today this is the only source of information on some events because documents have been lost.