1. Information from Gwynedd Archaeological Trust HER.

Summary
In June 1963, a hoard of metalwork was discovered on the western side of Nant Cader, next to a steep path which leads up from Tal-y-llyn. What appeared to be half-buried sheet bronze was noticed in a cavity below a large boulder protruding from the mountainside.

What had in fact been discovered was a hoard of bronze work, which mainly consisted of thin bronze decorated shield bosses, plaques and discs, they have been identified as typical of the Iron Age style known as 'La Tene' - a term used to define the so-called 'Celtic culture' which dates to the last six centuries BC.

The date of the Tal-y-llyn hoard has been a matter for debate. The decorative bronze work suggested a date in the Iron Age, but amongst the hoard was a piece of Roman bronze. This meant that the hoard could not have been deposited before AD 43. In addition to this, the decorative methods on some of the other bronzes used techniques that are only known to have been present at the very end of the pre-Roman Iron Age, and one of the items was made from brass rather than bronze. This was also very rare in the Iron Age. The objects are now in the National Museum of Wales.

Description :
A hoard of La Tene metalwork found by the footpath on the west side of Nant Cader in June 1963, consists mainly of fragments of decorated bronze sheet, some items tin-plated, packed tightly together, from at least two shields and other objects possible including a bier. All the pieces appear to be linked by similar decorative techniques and could be from the same workshop. Analysis of the metal in the second shield boss gives the possibility of mining of local ores in early Iron Age B. The hoard is dated to late 3rd/2nd century BC and shows a transitional phase of continental to native style in Britain. Now in NMW <1>

Spratling says that the types represented were still in circulation in Roman times and the deposition may be as late as C1st BC. <2>

Sources :
Savory, H. N. , 1964 , Bulletin of the Board of Celtic Studies, Part IV, May 1964, 449-75
Spratling, M. G. , 1966 , Antiquity , <2>
Savory, H. N. , 1964 , Antiquity , <3>
Darvill, T. , 1987 , Prehistoric Britain , <4>

2. Summary of the find from the National Museum Wales:
The plaque was found in 1963 on the slopes of Cadair Idris near Tal-y-llyn, Gwynedd by picnickers. The plaque was part of a hoard of tightly bundled metal objects, which had been placed beneath a boulder. The hoard also contained fragments from two shields, decorated plates possibly from a ceremonial cart and part of a Roman lock. This trapezoid shaped plaque is one of a pair. They are decorated with a design composed of an opposing pair of human faces, linked by a common neck. The faces have staring eyes, and finely combed hair, an image of striking quality. The head was widely venerated by the Celts. Could the Tal-y-llyn plaques represent a deity? Perhaps this was a hoard of scrap metal. Or was it a votive offering in response to an advancing Roman army? The plaque is made of brass, an alloy of copper and zinc. Brass production was a Roman technology. Objects of brass entered Britain before the Roman invasion and these could be formed into artefacts of Iron Age style. The plaque is about the length of a pencil and is very fragile.

3. Field visit by Toby Driver, RCAHMW, 11th December 2013. The find spot is marked by a prominent glacial boulder, naturally fallen into its present position and propped up on massive upright stones so as to resemble an artificial 'burial chamber'. Beneath the boulder is a dark, nartually formed 'chamber' which may have attracted Iron Age people to use the site as a place of deposition. The find spot lies alongside the modern Minffordd path up to Llyn Cau and Cadair Idris, suggesting considerable antiquity to this particular route. Across the path from the propped boulder, and below the line of the track, is a minor spring formed of rock slabs on three sides of a cleared, damp area. This spring head, if ancient, may have further influenced the hoard site. The boulder marking the find spot is the most prominent and impressive of its kind flanking the path as it ascends from the valley floor to the open mountain above. It is perhaps the only boulder formation which may have suggested an artificial construct or chamber to prehistoric people. It is likely that the corrie lake at Llyn Cau was the focus for any traveller climbing this path in antiquity, perhaps for ritual purposes, and therefore the attribution of the hoard to 'Tal-y-llyn' is potentially misleading in the interpretation of its landscape context.

T. Driver, RCAHMW, 2013.