I.
In the gods' great scramble for human followers, Nodens would seem to have lost decisively.
We know him only from vague inscriptions at two archaeological sites near the Welsh-English border. One might have been his temple. He seems to have been a Romano-British-Celtic god of . . . hunting? rivers? . . . worshipped around the Severn estuary between 100 and 400 AD. His cult may have been dispersed by Christianity, or could have faded away before that, a victim of ordinary religious churn. Roman paganism was Schumpeterian; innovate or be destroyed. Nodens didn't innovate.
Yet the more one looks, the less convinced one becomes that this is the whole story. Nodens was a river god; if you dam up a river in one spot, it will flow down other channels. Sometimes it will vanish underground, bursting out of some unexpected cavern miles away. Nodens was a hunter, and hunters know when to stay camouflaged.
In 1929, an archaeologist digging at the Temple of Nodens had some questions about the etymology of the god's name, and asked Oxford to send a linguist. Oxford dispatched a young philology professor with an encyclopedic knowledge of European mythology, who spotted a connection that had evaded previous scholars: Nodens appeared to be the same figure as the Irish god-hero Nuada of the Silver Arm. Nuada was king of the Tuatha de Danaan, a race of immortals who sailed from the north on ships that were clouds and made war against the then-inhabitants of Ireland, the Fir Bolg. He fought bravely, wielding his all-powerful Sword of Light, but in the climax of the battle, the Fir Bolg champion cut off his right arm. This caused some temporary trouble (the laws of the time prevented a one-armed man from being king), but his people were skilled at magic and metalworking, so they made him a new arm of silver, hence his epithet. He ruled for some number of centuries, a golden age of crafting and wonder-working, until the Tuatha de Danaan were invaded in turn (this was a theme; our source for these stories is a medieval manuscript called The Book Of Invasions). The new invaders banished Nuada's people to the hills and forests, where they became the sidhe aka fae aka fairies.