How would you memorise a speech with a palace? (its original use)

Put one key point at each locus along your route, then "walk" the palace as you speak, letting each place cue the next argument.

This is exactly what Roman orators did. Break the talk into its ordered points, place a vivid image for each at successive loci, and rehearse the walk. On stage you stroll the palace in your mind: the front door reminds you of the opening, the sofa of the third argument, the kitchen of the close. You get structure and order without notes, and you can never lose your place — the building holds it.