Pennannular brooches are common to many cultures. This particular style has been found in Viking silver hoards. I've seen Roman brooches of bronze. Convenient modern materials are copper (#6 wire, the size fastened to the pipes in your basement) and brass (3/32" brazing rod). You'll also need a hammer, a smooth block of metal, jewelers' pliers (preferably round-tipped), a file, and a gas flame. I'll illustrate using a propane torch, but I've also used gas kitchen stoves.
Use the pin to fasten a cloak at your right shoulder. This leaves your sword-arm free, just in case. Or take a square of cloth, a pin, and you have a shawl for those cold days.
Step 1: The body of the brooch
Take a piece of #6 copper, 5-1/4" long. Polish it, then bend into a circle with the ends about 1/4" apart.