Joinery: Simple mortise and tenon
This is the most basic, and likely the first, closed mortise connection. A version of this joint in stone and without a peg can be seen in Stonehenge. Beyond a doubt, it is the best connection for a vertical post to support a horizontal beam.
A timber frame for an average house, 1400 -1800 sq ft, would typically have 18–25 of these joints.