I sewed them out of muslin (dyed by the hubs … twice … to get a nice charcoal grey color), using Simplicity pattern #4059, which is in its Renaissance Costume Collection.
(I am thrilled I got this pattern 10 or so years ago and at such a good price! Joann’s Fabrics was holding its annual $1 pattern sale** and I bought about 30 patterns, about half of them suitable or specifically designed for costuming for men/boys/women. I saved a metric crap-ton of money. For instance, this pattern is marked at $16.95, but I only paid $1 plus tax! ** I don’t know if Joann’s still holds this sale, but I’m so glad they did then!)
The pants have one button, taken was from my stash of buttons. (Of course I have a button stash! Doesn’t everyone who sews have one?)