Many More Iron Age Shields from Britain, I M Stead, Antiquaries Journal 1991
Two recent british shield finds and their continental parallels, S Needham, Prehist 1979
Celtic Warriors, Ritchie, Shire 1997

The use of shields
Everyone in the period would use a shield as their primary form of defence. The shield and spear were the main weapon forms from the Greeks to the later anglo-saxons; two thousand years of history.
The use of two handed spears is a "re-enactorism" , encouraged by the fact that we don't throw or fire missiles at each other, and are rarely able to put together large enough numbers to reflect larger skirmishes.
In addition, massed cavalry charges are hardly a fact of Roman or British military warfare, the horses being relatively small and the use of the stirrup unknown. Long spear "blocks" appear in response to such cavalry tactics, used by the later Scots for example.

Everyone in the Vicus is expected to fight with a shield.

Shield Shapes

Based on finds within the UK, then the most common shield shape in Britain was possibly the "hide" shaped shield. This supposition does take into account the salisbury hoard of miniature shields and bronze edging as opposed to just complete finds.

This shield does seem to be peculiar to Britain and I am not sure why. It would be a handy shape to use within the context of the widespread use of the single hand spear. The cut outs certainly would aid in collecting and directing a spear thrust.

It is hard to tell the size of shields just from the votive offerings and edging found, however it is likely that the are of a similar size to the few bronze examples found, which is about 1.2m. 

Re-enactment copy of "hide shaped" shield (left)

In addition, there are images of smaller shields both square and round . These are very useful shields for individual style combat and for mobility. Pretty useless, it must be said, in any dense formation.

Ovals, hexagonal, rectangular and other larger "body" shields. These were to become the standard roman auxilia shield shapes in later times and their design and construction are very similar. The Image, left, is from the Arch at Orange and shows Gallic shield shapes. it also clearly shows the wooden spined and metal bossed examples.

All shields are of wooden construction, although a few (probably earlier) are solid bronze or have bronze facings.

Left and right. The Witham and Battersen shields, although these are bronze and considered 'parade' or 'display' shields as they are quite thin, it is entirely possible that they are facings for a wooden core and thus usable. Their shapes are consistent with those above.

British Shield Construction Notes: 
Body and small shields could obviously vary in size from person to person. A good guide is for a body shield to be tall enough for you to rest your arm across, which is just below nipple height. Obviously, the sizes of others can vary. The battersea and Witham shield are relatively small, when compared to the "body" shields, coming in at around 1.2m tall. Width of body shields can also vary a great deal, the Chertsey shield being 468mm wide and the Witham being approx. only 37.5cm (very narrow).

While round shields are shown from Gaul, it's hard to know whether these are popular in Britain at all. Its likely they were used as the shape is a common one from many earlier periods.

When painting a design onto your shield then limit yourself to period patterns. We recommend Early Celtic Designs as a very good source of patterns which are DATED. Stick to patterns that are dated to our period or slightly earlier, with some practice then it's easy to produce your own in the "style" of or to corrupt an existing one to fit onto the shield . Patterns dated to the 5th century BC are as anachronistic as using something from the book of Kells (5th century AD). 

Apart from the all bronze shields (like the Chertsey one) then I do not believe that any iron age shield has been found in this country with a metal handgrip. If you have the option then just use an applied wooden handgrip. an integral handle (like a Hjortspring one and some later roman examples) or one that is jointed in.

It is possible that most period shields have an applied rim of some description , either metal or sewn leather/hide.

For re-enactment purposes we insist on a rim as an unedged shield quickly turns into a splintered and dangerous mess after being exposed to our blunted metal weapons. It is group policy to try an avoid nailed dog chew rims on shields, unless disguised under a layer of cloth or leather. First choice would be a copper alloy rim, second choice would be an applied leather or hide rim that is _sewn_ to the the edge of the shield with linen or sinew (artificial sinew) thread. 

In addition, shields are also likely to have been faced with material to provide extra durability. While some shields would appear to be extremely thick, some are very thin indeed. In later periods, the addition of a leather or hide facing to a shield was intrinsic to it's construction and durability.
Shields have been found, close to our period, with a felt/wool cover and this, when soaked with glue and attached to the face of your shield is a very durable covering indeed. As a re-enactment group we will accept shields with no facing, a cloth facing using any period material (or one that is indistinguishable under a layer of glue and paint), leather or hide. All made using a suitable period construction.

Other Articles on shields:
Making a Shield 
Making a Scutum