The impending cold weather here in New York has spurred me on to start planning seriously for the Iron Age cloak idea I first hatched six months ago, in the beginning of summer. I’ve done a bunch of research and firmed up the plan for an ancient-inspired cloak!
This is a reproduction of scraps of a cloak found in Thorsberg Moor in what is now Northern Germany. It was probably a votive offering of some type, and was deposited in the bog some time around the 4th century AD. Details about fibers etc can be found here.
Now, this cloak is from a Germanic-speaking culture, and it’s also three centuries later than the specific period I’m focused on, the turn of the new millenia. However, the Greek writer Diodorus Siculus (who was basically an ancient travel writer… so by no means an anthropologically accurate recorder of foreign cultures), describes Celtic tribespeople in Gaul between 60 and 30 BC as wearing brightly colored checkered cloaks, similar to the cloak above. My guess is that this type of outer garment was probably not too dissimilar in Celtic-speaking pre-Roman cultures as well. So, with a little handwaving here and there (or a lot… alas), I’ve decided to go with the Angle cloak above as an inspiration for my cloak.
This description in Diodorus’s History of Gaulish clothing seems to indicate embroidery of some type, as well as “checkered” woven outer garments (aka plaid) that were brightly colored (at least to the Greek eye) and fastened with a brooch of some type at the neck.
Diodorus says (translation from here): “The way they dress is astonishing: they wear brightly coloured and embroidered shirts, with trousers called bracae and cloaks fastened at the shoulder with a brooch, heavy in winter, light in summer. These cloaks are striped or checkered in design, with the seperate checks close together and in various colours.” 
I’m not going to go for a completely brightly-colored cloak (I’m a New Yorker, and we wear a lot of black. It’s not likely that I would wear a vivid plaid on an everyday basis). I’m looking to weave one myself, however, using naturally diversely-colored, undyed wool from sheep similar to breeds native to the British Isles during the Iron Age. There are tons of options for breeds, which I’m looking forward to exploring next weekend at the Sheep and Wool festival in upstate New York. There you can see farms with heritage sheep breeds, some descendants of ancient breeds of sheep that were cultivated for wool in the Iron Age.
Some links for the interested:
So, just in case you were wondering, I am planning to be crazy and weave my own cloak, out of ancient-style heritage wool, into a plaid. It seems that there are a few breeds you could choose from, including these cute guys:
Ahhh! So cute! They are Hebridean Sheep from Scotland (of course). Look at their little faces! I like how they seem slightly menacing in this photo, like cute thugs thinking about beating you up. Ha ha. Another ancient breed (also cute… I suspect that might be a universal sheep trait) are Shetland Sheep, and there is a U.S. breeders association for them. One factor that will really make a difference is price. I think the cloak could get very expensive very fast, considering how large it is. The cloak from Northern Germany above was a gigantic rectangle: 5’6” x 8’… I’m making a wild assumption that its owner was 5’6” (but perhaps he was 6’ something, and the cloak was meant to be slightly longer than a human? It’s just that 5’6” is so specific…). If my cloak is to be body height x 8”, it would be 5’4” x 8’ (alas - to be shorter than Germanic tribespeople). So, this is still in the idea stage, financially, until I figure out how much wool I’d actually need for such a thing…
In any case, the general plan is to somehow find a modern loom that is capable of weaving a 5’4” x 8’ square of plaid fabric. Buying a fancy loom is out of the question because of price! So I’ll try to find one I can rent time on somewhere, or borrow time on (?)… or plan B is to hit home depot and construct a warp-weighted period correct loom (note: no examples have been found of looms in the British Isles, as far as I know, from the Iron Age, so this is more hand-waving based on Germanic examples). They seem really cool and probably relatively easy to build, but the obvious downside is that it would probably take about 500 years to weave a huge rectangle of plaid fabric….! Another idea is to build a modern-ish loom out of PVC with the use of this ingenious book, which would help me to actually get my cloak finished before winter rolls around. Most of these looms are smaller than 66” in width, meaning that I’d have to weave together a few smaller 8’ pieces to form the final cloak. I think I’m fine with that (we have to compromise, and not having a gigantic loom in our small Brooklyn apartment is probably a good compromise).
Warp-weighted loom with weavers using an antler beater bar, from here.
More information about looms and weaving:
Lastly, my plan is still to embroider some Celtic knotwork designs on top of the finished woven fabric. So that it stands out, I’ll probably embroider these using wool dyed with woad. You can buy a bunch of awesome woad-dyed wool here, as well as buying the woad to do your own dying (warning: it’s horrifyingly smelly; in fact, woad dying was banned from urban areas in Tudor England!)
Anyway, there you have it. Am I completely crazy? Probably. I’ll still have to see if this plan is even financially feasible with all the wool that is required! My dear friend and conspirator Eva has wisely suggested that I make a series of cloaks — the first made from purchased fabric, to test the size and shape of the cloak, and placement of embroidery, the second woven on a modern loom, and the third cloak — a testament to the wearer’s insanity — loom woven on a warp-weighted authentic loom.
Regardless of potential obstacles, how awesome would it be to have your own Iron Age-inspired Celtic cloak woven from heritage wool, that you wove yourself (possibly on a DIY loom constructed in the fashion of ancient looms from that region), with ancient knotwork designs embroidered on top of it in wool dyed with woad!? Answer: totally awesome.
 Iron Age Celtic-speaking societies, as far as I know, mainly relied on memorized oral traditions which were lost after their conquest by Rome, and left almost no indigenous written records. This leaves us with only a few ways of learning about them: sketchy Roman etc. travel writing and/or accounts of people they were in the process of conquering, occasionally an archaeological find, and vague and dubious guessing from folk customs or indigenous written material from a much later date (post-Christianization).
 You can read the whole book by Diodorus here, although in a different translation.