It is probably this one:
Ref Antoninus Pius AE Sestertius, RIC 929, Cohen 543, BMC 1863note
Antoninus Pius ? Sestertius. ANTONINVS AVG PIVS P P TR P XVIII, laureate head right / LIBERTAS COS IIII S C, Libertas standing left holding purse and extending hand. Cohen 543.
The coin was minted 154/155 A.D.
Amber way was from Roman Imperium to Baltic Sea (on Polish teritory from mountains) .
There are about 100-200 Roman coins found each year.
I've found 5 denarius and 2 sesterces so far.
Very big treasure Roman coins were found on Nietulisko, over 4000 denadius in one place.