One of the simplest training tools for practicing strikes in Renaissance martial arts was the pell. The pell was an ancient training device for practicing swordplay and training soldiers in arms. It typically served as a practice target for striking with a shield and a wooden sword. A pell is something like the Medieval equivalent of a boxer’s punching bag. It consists of an ordinary wooden post or tree trunk planted firmly in the ground. A pell might be man-height and roughly six to twelve inches in diameter.
— J. Clements, On The Pell
This article got me started with pell works. While a pell does not replace a proper sparring partner some techniques can be trained on a pell. More on this topic can be read on Essential Training: The Pell by Stewart Feil.