Thinking further about Kalefeld and its implications for Roman involvement deep into Germany as late as the 3rd century, I was reminded of this project on Ptolemy's mapping of Germania Magna. Taken at face value (which the researcher's seem to have done) the map suggests quite detailed knowledge of peoples and places as far east as the River Vistula in modern Poland.
Not the first attempt to 'correct' Ptolemy (see eg Strang in Britannia 1997). All such depend on an assumption that his information was reliable, and essentially accurate, and that systematic errors can be identified and corrected for. Not easy assumptions. In fact Germania Magna provides a case in point (noted as long ago as 1917). The first two places listed are evidently lifted from Tacitus (not what you'd call a geographic text), the second entirely imaginary, but both confidently provided with coordinates.
First we get Φληούμ (Flevum), closely followed by Σιατουτάνδα (Siatutanda). Turn to Tacitus Annals 4.72-74 and you will find description of the Frisian revolt of AD28. Reinforcements arrive to the relief of Flevum castellum only to find that the Frisians have retired 'ad sua tutanda' - 'to protect their homesteads'. It seems very much as if a Greek speaking compiler has not understood this phrase and has just lifted two supposed places from here and placed them on the map. The fact that an imaginary place can be provided with coordinates casts doubt over any place within his text for which we lack independent confirmation. Even if Ptolomy was correctly informed of the names of places within 'free' Germany, we cannot necessarily assume that his locational information was accurate.
