I uploaded some more images from the Met today and among them are several images of a bronze three-horned bull (unfortunately the center horn is missing) that was recovered from Octodurus, a city founded by the Emperor Claudius, in Switzerland.
It's a wonderful sculpture and I'm so glad the piece was not melted down as it appears to be part of a statue that had been rendered apart in preparation for scrapping. It made me curious about the worship of a three-horned bull so I researched it further and learned that the three-horned bull, sometimes called Tarvos trigaranus, was worshiped by the Celts in Gaul and Britain.
According to an article by Susan Read, Martin Henig, and Leslie Cram that appeared in the journal Brittania, art depicting three-horned bulls was common in northeastern Gaul. They said it seems to have been derived from statues of two-horned bulls from Campania that were constructed with a crescent between their horns. They mention four such statues found in Britain - one in Maiden Castle at Dorset, one from the Jewry Wall Site in Leicester, one from Southbroom near Devizes in Wiltshire, and the last a pipeclay figurine, "certainly an import from Gaul", found at Colcester.
I also read an interesting description of a divination to determine a new Celtic king using a bull.
"Bulls were used in divination in both Ireland and Scotland. At Tara a new king might be chosen in the tarbfheis, `bull-feast' or `bull-sleep', in which a bull was killed and a man ate his fill of its flesh, drank its broth, and then lay down to sleep. After an incantation had been chanted over him by four druids, the dreamer would know the new king in his dream. In Scotland a person might answer an important question about the future (no king was to be selected) by wrapping himself in the warm, smoking hide of a newly slain bull in a remote place, such as near a waterfall. Upon going into a trance the person would have the answer. This method was known as taghairm." - Celtic Mythology, Oxford University Press.
Apparently the three-horned bull even found its way to the standards of the Roman Legions:
"...standards of ala Longiniana (CIL XI11 8094) and cohors I Gallica (ILS 9127) appear to have been adorned with animals popular in Gallic religious
iconography - respectively, a three-horned bull (Green 1976, 13) and a small boar.6 Such animals almost certainly appeared on signa of the type referred to by Tacitus (Germ. 7; Hist. 4.22), borne by the pagi and tribal groupings of the Gauls (Royrnans 1990,19). They appear open to different symbolic interpretations: depending on the cultural perspective of the viewer, they could have been seen primarily as traditional Gallic tribal totems or as Roman military regimental standards." - The Roman Army As A Community .