There were a wide variety of helmets in use in the mid-first Century, nowadays known by H. Russell Robinson's classifications (see his Armour of Imperial Rome for the fullest details). The choice of style is up to you.
The quality of your helmet must be quite good. Roman helmets were forged in one piece complete with neck guard; reproductions may have welds if they are not visible on the outside. All the appropriate ridges and fittings must be present. Generally, steel is used instead of iron, and either yellow or red brass is fine (the zinc content of Roman brass or "orichalcum" varied).
Of the Imperial-Gallic helmets, type G is the most popular with reenactors, but types A through I are all acceptable. Type I is brass, type A can be iron or brass, while the rest were apparently all iron. All have embossed steps and ridges on the back of the skull, neck guard, and cheekpieces, and the distinctive "eyebrows" on the front. (The outer step on the neckguard is indented in the center.) The brow reinforce is an iron strip, or brass on brass helmets.
All Imperial-Gallic helmets except type A have applied brass features; edging, stamped decorative bosses, "reeded" browbands, crest support holders and hooks or rings, chinstrap rings (one under the neckguard, one inside each cheekpiece), and sometimes carrying handles. Types E-I have earguards of brass, while type D's are of iron, and types A and C have none at all. Applied brasswork is often tinned or silvered.
The applicable Imperial-Italic helmets, types B, C, and D are quite similar to the Imperial-Gallic, but have no eyebrows and few decorative bosses, if any. The brow reinforce is usually thinner than on the Gallic types, often with the front edge turned down for strength. Type D has brass earguards, but on B and C the edges of the ear cutouts are simply flanged outwards. The Italic crest support holder is a raised disc with a slot, rather than the Gallic flat rectangular tube.
Coolus (types C-I) and Montefortino (types C-F) helmets are brass and fairly plain, except for some ridges or raised panels on the cheekpieces. They are globular or hemispherical in shape, not closely fitted to the head like the Imperial types; some were spun on a lathe rather than hammered to shape. The brow reinforce, not present on some Montefortino types, is either flat or has a turned-down edge. There is usually a crest knob, made in one piece with the skull on a Montefortino, but soldered or riveted onto a Coolus, and there may be feather tubes at the temples. Chinstrap rings are identical to Imperial helmets, although earlier examples have studs outside the cheekpieces instead. There are no earguards, bosses, edging, or reeded browbands (although Coolus type H has filed decoration to resemble a browband). Bronze helmets may be entirely tinned or silvered.
Fittings and Details
Decorative bosses are usually stamped out of thin brass (0.01") , and a number of designs are known. Some examples are silver with red enameled centers. "Reeded" brow bands were cast, but modern reproductions are often stamped. Earguards, whether of brass or iron, should at least appear to be made in one piece, even if welded or soldered. Coolus-type crest knobs may be turned or cast, while Imperial crest holders are made of sheet brass. Brass hooks or rings for securing the crest are also present on most Imperial-style helmets.
Most Imperial helmets have brass edging on the cheekpieces and neckguard, which can be made from 1/8" to 3/16" tube. Anneal well and bend to fit, re-heating if necessary to avoid bad puckers. Then slit the tube open around the inside with a dremel tool and fit it into place, and hammer carefully to flatten it. Brass tabs approximately 1/4" wide may be riveted on to secure the edging if needed; 2 on each cheekpiece and 2 or 3 on the neckguard. The edging might also be made from a brass strip approximately 3/8" wide, instead of a tube.
Examples of brass carrying handles seem to date to the second half of the 1st Century. They are secured by 2 brass split pins, rather like cotter pins.
Chinstrap rings are approximately 1/2" in diameter, each secured with a brass strip folded double and riveted in place. There is one under the center of the neckguard and one inside each cheekpiece, near the bottom. The chinstrap thongs start at the neckguard ring, cross under the throat, and are passed through the cheekpiece rings to be tied under the chin. Coolus and Montefortino helmets, up to type C, and Imperial-Gallic type A have projecting studs on the cheekpieces instead of rings. Normal thongs can be looped around these and tied under the chin, or wider straps can be used, with slits to "button" over the studs.
Helmet linings were usually glued in place (with hide glue), but little is known beyond that. Patterns are available for a simple linen cap which can be padded with cotton batting, horsehair, tow, fleece, scraps, etc. It can be made adjustable with a drawstring. Thick felt can also be used. The lining can be sewn to a leather band which is then glued into place, so that the lining can be removed for washing or repairs just be cutting the stitching.
While the Twentieth Legion's setting is the mid-1st Century AD, you may wish to slant your appearance towards the beginning or end of that time-frame. Some helmet types, such as Imperial-Gallic I and Italic types C and D, are thought to date to the second half of the century, and were possibly not in use during the invasion of Britain in 43. Coolus and Montefortino helmets, on the other hand, were being superceded by Imperial styles during our period, and would have been much less common by the time of Boudicca's Revolt. (It is believed that many were relagated to the auxiliaries.) Other than that, it is impossible to say just what types of helmets were or were not used by the original Legio XX, so we can, and should, display a wide variety of those in use at the time, for educational purposes. Helmet Crests
crested helmetThere are depictions of helmet crests and a few descriptions, but no surviving examples or fragments (besides the metal attachments). It is believed that crests were not worn in battle in the 1st Century AD except by centurions. Legio XX has chosen red for the color of their crests, though they may be of different styles. The first type described is for Imperial-style helmets.
The crest block is wood, approximately 1 1/2" wide by 1 1/4" thick in height. (It can be cut from a nice 2x6.) The exact size and shape depend on your helmet and preferences, but it is approximately semi-circular. The ends should not quite touch the helmet at the attachment points at front and back, and the center is 1 1/2" to 2" above the crown, supported by the crest support. The placement of the central support and its holder will also influence the crest's shape. (For instance, is the support inserted into the front of the holder or the rear?) Make a cardboard pattern first to be sure of the shape.
Cut the block out carefully and sand it well. Mark the locations for the holes, 1/4" in diameter, 1/4" apart (1/2" on the center), and approximately 3/8" deep. Three staggered rows work well. There can be about 100 holes. Drill them carefully, as the wood grain may cause the drill to drift off-target. When the holes are done, sand the top of the block again and paint the whole thing red. You may add carved, painted, or applied decoration to the block.
About 8 ounces of white horsehair is needed. (One ounce will make 12 to 14 twelve-inch tufts.) Cut it to about 12" long, separate it into about four bundles tied tightly in the middle, and dye it red with Rit Scarlet fabric dye in a large kettle on the stove (follow the directions!). Do not substitute leather dye as it is not waterproof. Lay the hair flat and straight and allow to dry. When dry, separate the hair into as many little tufts as there are holes in your block, and tie each tuft in the center with heavy thread. Don'y worry about the white middles of the strands. Fold each tuft in half and glue into a hole. When the glue is dry, comb the hair gently with a fork or coarse comb and give it a light trim.
Feathers can be used instead of horsehair, and red ones are available from Tandy Leather and various craft stores. They may have to be trimmed a couple of inches. If your helmet has feather tubes at the sides you may wear a feather in each of them, no matter what your crest is made of.
The crest support for an Imperial-Gallic helmet can be cut from a square-section 1/4" brass or steel rod 5" to 6" long. Make a 2" cut in one end with a hacksaw, and bend the arms down to a T-shape. Then bend up each arm so that your crest block fits between them, and finish the tips by curling them down. Anneal the metal before each step. Making sure that the center post is the right height to support the crest where you want it, bend the bottom end to form the foot or tongue, and grind or hammer it flat to fit the holder on your helmet. Finally, file, sand, and polish it well. The arms can be squeezed slightly at the top to give them a firm grip on the crest block.
Imperial-Italic helmets have "twist-on" supports, usually cast; a T-shaped stud on the bottom fits into the slotted disc on the helmet and secures with a quarter-turn. Some have a spike between the arms which would fit into a hole in the crest block; this could be secure enough to dispense with hooks or rings.
Many depictions show a comparatively short block mounted directly on the helmet. Judging by the archaeological evidence this would not be the most common style, but a U-shaped support with a T-stud on the bottom has been found. This would result in a "flush-mounted" crest similar to those illustrations, and is an option for some Italic helmets.
Coolus helmet crest knobs often have a slot crossed by a hole. A metal tongue on the bottom of the crest block (or set into a conical hole) fits into the slot and is secured by a pin. The crest block would be quite short in this case. There is also evidence that some Coolus helmets carried a longer crest (approximately 1/3 of a circle), anchored to the knob near its front end, while at the back a metal tongue was slid under a strip riveted to the skull just above the neckguard.
Montefortino helmets generally have a knob with a vertical hole. While a Coolus-style crest could be "retro-fitted" to this, it was designed to accept a pin on a simple plume or "tail" of horsehair.
While you will probably want to display your crest when not in use, it is better to store it carefully. It is one item of equipment which should not show wear and tear from campaigning. Keeping it covered and laid flat-- or better yet, suspended upside-down-- will keep dust off and prevent drooping. The best option is to construct a sturdy cardboard box with strings or wire twist-ties inside to keep the crest from sliding around. Make a place for the crest holder, too.