Probably Trier, 4th-6th century 
Rock crystal, 13 cm

Found in a tomb on the banks of the Rhine, these magnificent rock crystal lions' heads — together with an ivory plaque found with them — were thought to have come from a third- or fourth-century imperial chair or throne. Even though it has now been recognized that the lions' heads were carved at least a century earlier than the ivory plaque, their size and hollow interiors seem to support this view. Among the many uses of carved precious and semiprecious stones, this function seems the most plausible. 
Although these are the only crystal lions' heads to have survived, monuments of the fourth to sixth century provide ample evidence that lions' heads were used on contemporary thrones. They appear on the top of the back uprights on the Hetoimasia throne in the early fifth-century mosaic of Basilica of Santa Maria Maggiore in Rome and on the imperial throne of the personification of Rome on the coins of Gratian, Valentinian, Theodosius, and Honorius. The fact that these heads were found on the banks of the Rhine has led to the proposal that they were carved in Trier. Evidence that there was a workshop in Trier is provided by the agate bowl in Vienna, which is carved and signed by a Trier artist.
Although less plausible, it may be that these heads once adorned a sella curulis of the sixth century — for at that time the consul's chair became more ornate: the cabriole legs of the seat now terminated in lions' paws, and lions' heads became a usual component of the decoration below the front seat rail. This association of lions with the sella curulis may have come about under the influence of Christian ideas, since, through its association with the throne of Solomon — just king par excellence — the lion is the emblem of justice. By the mid-sixth century the emperor, who was considered to be God's representative on earth, had absorbed the office of the consul, and much of the ritual of the consular ceremonies had been Christianized.