The date is from the name of the official (monetal or moneyer) C. Antestius. T.R.S. Broughton's Magistrates of the Roman Republic puts him between 137 and 134 B.C., but that work was published in 1952, and perhaps new information has come out since then to show that he was actually in office in 146 B.C.
In Brian Sykes book, "Saxons, Vikings And Celts", he thinks he's found a small DNA group that he believes could relate to the Roman occupation.