By the time of Tacitus, the Aestii have emerged. The former Scythia was now entirely Sarmatia. Evidently the Sarmatians conquered westward to the Vistula. The Goths moved to the south. That the Balts lived east of the Vistula from remote prehistoric times is unquestioned. The Baltic languages, however, are only known from the 2nd millennium AD. They are known to have developed in tribal contexts, as they were originally tribal. The first mention of any tribes is in Ptolemy's description of European Sarmatia, where the main Prussian tribes are mentioned for the first time. In Tacitus, only the language of the Aestii is mentioned. Strabo distinguished the Venedi, who were likely Slavs. From these few references, which are the only surviving evidence apart from glottochronology and place name analysis, it would seem that the Balts of Pytheas' time were well past the Common Balto-Slavic stage, and likely spoke a number of related dialects. By turning back at what he thought was the limit of Germany, he not only missed the Balts, but did not discover that more Germans, the Goths, had moved into the Baltic area.