Apollo Maponos
Apollo "Great Divine Son"

A god attested to in both Britain and Gaul, with presumed cognates in medieval Welsh, Irish, and French literature.

Maponos means "Divine Youth", deriving from the Gaulish (and Brittonic) mapos, "boy", with the -on- divinizing partical. Considering his name and that he is conflated with Apollo in some Roman inscriptions, Maponos appears to be the personification of youth.

He may have originally been a god of the Parisii; they lived along the Marne (as well as the Seine), and later some may have migrated to Britain, where there is found another Parisii tribe in the area of Yorkshire. This area, adjacent to what became the kingdom of Rheged, may explain the relationship between Mabon and Owain ap Urien.

Inscriptions
At least four inscriptions to Maponos refer to him as Apollo:

RIB 1120 (Corbridge): Apollini Mapono Q Terentius Q F OVF Firmus Saen Praef Castr Leg VI VPFDD
"To Apollo Maponus, Quintus Terentius Firmus, son of Quintus, of the Aufentine voting tribe from Saena, Praefectus Castrorum of Legio Sextae Victrix Pia Fidelis, donated out of devotion"

RIB 1121 (Corbridge): Deo Mapono Apolloni P AE [...]lus / Leg VI Vic VSLM "To the god Maponus Apollo, Publius Ae[lius Lucul]lus, centurion of the victorius Sixth Legion, willingly and deservedly fulfills his vow"

RIB 1122 (Corbridge): [Deo] / [M]apo[no] / Apo[llini]
To the god Maponos Apollo

RIB 583 (Ribchester): Deo san(cto) / [A]pollini Mapono
To the divine god Apollo Maponos¹

Two inscriptions refer to him only as Maponos:

RIG L-100: Chamalières: Mapon Aruernatin
Maponos of the Arverni?

AE 1975, 00568: Chesterholm (Vindolanda): Deo Mapono
To the god Maponos

And it apparently was used as a personal name:

• CIL 13, 05924: Bourbonne-les-Bains: Maponus / histrior ocaba /tus decessit ann(orum) XXX
  Maponus the actor, dead at age 30.
• CIL 13, 10010 1262: used as a potter's mark, presumably the potter's name.

Finally, there might be mention of him on the Coligny Calendar, where the 15th day of the month of Riuos is marked with the word "Mapanos". Whether this refers to a feast of Maponos isn't clear, but it is certainly possible.

There are three statues to him; the first depicts a young man with a harp, which would identify him with Apollo Kitharedos; on the other side of the altar depicts Diana the huntress, though whether she represents Diana or an interpretation of a local goddess is unknown. A sketch of this is found in Ann Ross's Pagan Celtic Britain. The second statue is identified by Ross, and found on the cover of Patrick Ford's The Mabinogi; it's appearance is blocky and has a beard, not a youthful face. The third, identified as Maponos by Birley,

Identification with Apollo
As noted, Maponos was identified with Apollo; one depiction identifies him with Apollo the Harper, but mediaeval tradition also identifies him (i.e. Mabon) as the greatest hunter in Britain, and probably also reflects Apollo's role as a hunter. Finally, if the spring at the mediaeval fonto Mabono refers to Maponos the god, then it may also identifies him with Apollo's role as a healer, springs generally associated with healing centers.

Later Tradition:
Maponos is generally agreed to be the origin of Mabon ap Modron in Welsh legend. Modron is derived from Matrona, goddess of the Marne River in France, whose name means "mother." The grave of an actor named Maponus at Bourbonne-les-Bains, near the Marne, may indicate that the same worship of Maponos the god was present in the area, and a relationship between Matrona and Maponos was present in Gaulish belief, though this is so far the only known example, and an extremely tenuous one at that.

Maponos was a god of the Parisii. Corbridge, where three inscriptions to Maponos are found, is in Northumberland, and Chesterholm and Ribchester in Lancastershire--both areas near the Parisii settlements in Britain, and both adjacent to what became medieval Rheged. The town of Locus Maponi, mentioned in the Ravena Cosmography, is likely modern Lochmaben, which is in the county of Dumfries and Galloway, bordering modern Cumberland, part of Rheged. Essentially, his worship seems to have centered in northern England/southern Scotland.

The significance of this is found in several stories regarding Urien and his son Owain, which mention Mabon and Modron. In a story from Peniarth 147, it is told that Urien's children were sired on Modron, daughter of the king of Annwfn. In a poem attributed to Taliesin, Owain is apparently identified with Mabon. It is possible, as John T. Koch notes in The Celtic Heroic Age, that the story of Urien having children with Modron may go back to a sovereignty rite, as is found in Irish literature. That all of these post-Roman associations happen in the area where Maponos was worshipped is not an accident. Maponos simply became Mabon as the language mutated.

The question, of course, is that although Maponos and Mabon are to be identified with each other, it is unknown how much of Mabon's mythology reflects beliefs about Maponos.

In Welsh literature, Mabon is stolen from his mother when three days old, and held prisoner at Caer Lowy, "Gloucester", but with the added meaning of "city of light." He can only be found by asking the oldest animal, and is also said to be a great hunter.

In Irish tradition, Maponos is apparently connected to Oengus Mac ind-Og, whose name means "Oengus the Son of Youth", son of the Dagda and the river goddess Boann. Like Mabon, his birth is strange--the Dagda makes Samhain last for an entire year, so that Oengus can gestate and be born in a single day. Also, Oengus is associated with the famous Newgrange monument, with its famous Winter Solstice alignment. Now, whether Oengus was associated with Newgrange because Maponos had an association with the winter solstice, or if the associate's reason was more osbscure, is hard to tell. The winter solstice is never explicitly mentioned in any text concerning Mabon or Oengus.

Possible Significance: Comparative Mythology
If Matrona was ever considered Maponos' mother (we unfortunately have no myths about Maponos himself), and if we assume that Maponos and Mabon had similar mythologies, then Maponos' father was likely the god of lightning, as Mabon's father is apparently Mellt, the Welsh word for lightning. The reconstructed name would be *Meldos, though there are other possible names. If true, Maponos/Mabon represents an essential element of Indo-European cosmology--the god of fire in water (*Meldos and Matrona). This fire-in-water parentage is also seen in Maponos' Irish reflex, Oengus, son of the Dagda (called Aed, fire, in some texts) and the river goddess Boann, one of several fire-water couplings in Celtic (and Indo-European) mythology.

Literature:
Maponos does not appear in any true literature; however, his Welsh counterpart Mabon appears in several texts--"Culhwch ac Olwen", "Pa Gur", "Englynion y Beddau" and the lost "Lai du Mabon".

In Chretien de Troyes' Erec, Mabon/Maponos appears as an imprisioned knight named Mabonagrain, while in Ulrich Lanzelet, he is Mabuz, son of the Lady of the Lake. Both Mabonagrain and Mabuz are likely derived from Mabon via the Bretons and not directly from Maponos.

Oengus appears in several Irish texts.

NOTES
1. The inscription in full, dated to 238-41 CE:

Deo san(cto) / [A]pollini Mapono / [pr]o salute d(omini) n(ostri) / [et] n(umeri) eq(uitum) Sar/[m(atarum)] Bremetenn(acensium) / [G]ordiani / [A]el(ius) Antoni/nus |(centurio) leg(ionis) VI / vic(tricis) domo / Melitenis / praep(ositus) et pr(aefectus) / v(otum) s(olvit) l(ibens) m(erito) / [de]dic(atum) pr(idie) Kal(endas) Sep(tembres) / [Im]p(eratore) d(omino) n(ostro) Gord[i]/[ano A]ug(usto) II e[t] Pon[peia]no(!) co(n)s(ulibus)

To the god Apollo Maponos, for the health of our lord, and of Gordian's Calvary of Sarmatians of Bremetennacum--Aelius Antoninus, centurion of the Sixth Legion Victrix, from Melitene, commandant of the contingent of the region, willingly and deservedly in fulfilment of a vow, dedicate this on the 29th of August, during the reign of our lord emperor Gordianus Augustus II and the counsul (Clodius) Pompeianus.