Follis. Constantine X and Eudoxia, 1059–1067.
Invisible caption.
Christ standing frontally, holding the Bible.
Begtimurid of Akhlat countermark in three Arabic letters (sin, lam, alif). Akhlat workshop.
The countermark is visible near the centre on the left.
Begtimurid of Akhlat 1183–1193 was part of a Seljuk dynasty.

The justification for a countermark is, until now, controversial. It ranges from a change in face value, whether up or down, to the geographical extension of the currency, to the integration of the currency of the vanquished into that of the victor. Until proven otherwise, none of these hypotheses is dominant.
Unless each one is applicable in a specific case.