This silver reliquary head of Saint Alexander clearly reflects the influence of ancient Roman culture. The realistic size of the head, its idealized depiction, as well as the characteristic hairstyle, only apparently untidy and with locks of symmetrical curls combed forward and covering part of the forehead, recall portraits of young Roman emperors such as Augustus and Constantine. This does not come as a surprise, since one of the main artistic influences of Romanesque art was ancient Roman art.
It is also possible to refer to the influence of Byzantine art in the plaques that decorate the stand where the head sits, but I will not elaborate on this, since the question is referring primarily to the bust.