The medieval period was also known as the Middle Ages which dated from 1100AD -1499AD. Stories from the medieval period evoke images of brave knights and damsels in distress. You can make a costume from the time period by using natural colours and fabrics. Visit local thrift stores to find some of these pieces.
The best dressed women of the Medieval were the Queen's ladies. They wore fitted gowns that reached to their ankles. The sleeves and skirt had a bell shape. You should choose or make a gown in natural colours like sky blue or a woodsy brown. The popular colour according to history was forest green. A shorter sleeveless tunic is worn with the dress for fancier occasion. Create a criss-cross effect over the bosom with some embroidery cord. Add some to the sleeves to on the upper arm. She could wear a simple veil to cover the back of her hair. Or you could wear a pointy hat covered in light fabric. She might also wear a long necklace with a pretty imitation stone or some fake jewelled rings.
Medieval gentlemen, when not wearing suits of armour, wore a tunic and hose. Tunics could come to the mid thigh or even touch the ankle. Robes could be worn the same length as the tunic. Pointy toed slippers and hose were the finishing touches of a gentleman's outfit. He wore colours similar to the ladies. Blues, browns, greys and even whites. Scarlet or purple however was reserved for kings and queens. Gentlemen wore a variety of hats and some had decorative feathers.
One of the most troubling occupations of the romantic Middle Ages is that of the executioner. During this period there was a lot of religious persecution which was where an executioner could find employment. This scary Halloween costume is a classic. You'll need a shiny black tunic that goes to the floor. You'll wear black hose and black leather shoes. You could wear a wide black belt cinched at the waist. Add a skull shaped stone or embellishment to the buckle. Make a hood out of a black pillowcase. Shape it with safety pins and cut out eyes and mouth holes. Carry around a rubber executioner's weapon for chopping off a head or two.