It was long thought that the most common stitch on early modern garments was the running stitch. Recent re-examinations have shown that this is inaccurate.
Those who have tried to sew their replica garments using only running stitches will not be surprised. Even if one makes the stitches 2mm to 4mm apart, the running stitch simply isn’t strong enough to take the strain.
However, there is a stitch that could be mistaken for a simple running stitch and yet would create a far stronger seam. In Elsestergaard’s book on the medieval Greenland finds, Woven into the Earth, she explains that the seams were sewn from the right (out) side with an almost invisible stitch executed by turning the seam allowance toward the inside and making a blindstitch between the outer surface of the fabric and the folded edge of the seam allowance. In practice, this creates a line of stitches that look very much like running stitches except that they are ever-so-slightly tilted from the vertical. The use of this stitch on a seam creates a very strong join. This stitching technique did not pass away at the end of the Middle Ages and can be found on garments from the 16th and 17th centuries.
A good stitch is a good stitch.