The chronicle of Thietmar poses some problems of interpretation of the information regarding the attack of Margrave Gero on the Slavic tribes, as a result of which he purportedly
subordinated to the authority of the Emperor Lusatia and the Selpuli (meaning the Słupian tribes)
and also Mieszko with his subjects. According to the majority of modern historians,
[16] Thietmar made an error summarizing the chronicle of Widukind, placing the Gero raid there instead of the fighting that Mieszko conducted at that time against Wichmann the Younger. Other sources make no mention of such conquest and of putting the Polans state on the same footing with the Polabian Slavs. On the other hand, the supporters of the Gero's invasion theory
[17] believe that the Margrave did actually carry out a successful invasion, as a result of which Mieszko I was forced to pay tribute to
the Emperor and also was compelled to adopt Christianity through the German Church. The thesis that proposes the introduction of Christianity as a result of this war finds no confirmation in German sources.
The homage is then a separate issue, since, according to the chronicle of Thietmar, Mieszko actually paid tribute to the Emperor from the lands
usque in Vurta fluvium (up to the
Warta River).
[18] In all probability Mieszko decided to pay tribute in order to avoid an invasion similar to the one that Lusatia had suffered. This homage would take place in 965, or in 966 at the latest. Very likely the tribute applied only to the
Lubusz land, which was in the German sphere of influence.
[19] This understanding of the tribute issue explains why already in 967 Mieszko I was described in the Saxon chronicles as the Emperor's friend (or ally, supporter,
Latin:
amicus imperatoris).