There is not really much to be seen on this stone. That is because it has spent decades exposed to the erosive conditions near the hottest thermal fountain of Wiesbaden and, as a consequence, has decayed more that its original that is kept in our museum. The inscription reads:
Antonia Postuma / T(iti) Porci Rufiani leg(ati) / [l]eg(ionis) XXII P(rimigeniae) P(iae) F(idelis) [pro sa]lu/te Porciae Rufianae / filiae suae Dianae Mat/tiacae [ex] voto / signum posu[it]
Antonia Postuma, wife of Titus Porcius Rufianus, Legate of the 22nd Legion called P(rimigeniae) P(iae) F(idelis), has dedicated this memorial to Diana Mattiaca to commemorate the healing of her daughter Porcia Rufiana.
The 22nd legion had its base camp or rather fortress (castra) in Mogontiacum, modern Mainz, opposite the river Rhine about 6 km from where the stone was found. Rufianus was evidently a member of the ancient senatorial House of Porcii that had produced Cato the Elder as one of its most illustrious descendants, but that is all we know about him, and the genealogical tables of the Porcii do not include him nor his wife and daughter. There is no information on the nature of Rufiana's illness.
As elusive is the goddess Diana Mattiaca who is not attested in any other inscription. At least the reference to the name of the town, Aquae Mattiacorum, is evident - the Mattiaci had been the local Germanic tribe; according to Tacitus they were a splinter group of the mighty Chatti. But why would they have need for their own special Diana?
In her case I have a hypothesis: I believe that Diana Mattiaca is a camouflage of Sirona, otherwise known in Wiesbaden from the dedication by Iulius Restitutus, described below on this blog. Sirona has often been depicted with a male consort, Grannos, and in the Interpretatio Romana, the pair of them were commonly switched into Diana & Apollo (especially when Sirona's aspect as goddess of the moon and the nightly sky came into play). Postuma may have considered it inappropriate for a senatorial lady to revere a barbarian goddess; hence, Diana Mattiaca may have been made up ad hoc to mention Sirona in a way that the Roman high society would find acceptable.
If that is true, then Legatus Porcius Rufianus may actually have met Iulius Restitutus, curator of Sirona's temple, from the other inscription that had been found not too far away.
The potential consequences of their meeting, and the "disease" his daughter was to be cured from, we have elaborated on in the first story arc of our novel series, Romanike. I hope Rufianus' immortal soul will forgive us that we have twisted him into the most ruthless villain of our entire cast. ;-)