The article is devoted to the publication of an inscription found in Tanais, which speaks about the erection of a statue of the Bosporan king Sauromates III (AD 229/230–231/232). The statue was commanded by a person whose name is disappeared and only the patronymic (the son of Asandros) is preserved; he was a commander of a «Thracian detachment and a square of hoplites». A similar connection is mentioned in the funerary oration SEG 55, 862 from Panticapaeum which allows me to suggest a chronological vicinity of two inscriptions and confirms the date of the second one in the end of the 2nd or the fist half of the 3rd century AD proposed earlier by G. Bowersock and C.P. Jones (the reign of Sauromates III rather than Sauromates II). An analysis of these and other inscriptions mentioning the «Thracian detachment» allows to interpret this detachment as the Roman auxiliary cohors I Thracum. The soldiers of this cohort were probably sent to the Bosporus from the province of Lower Moesia (not from Bythinia–Pontus, as it was suggested earlier) together with those of legio I Italica who participated in the «Bosporan war» mentioned in an inscription from Preslav.