Horizontally. The square forming the new base of the upper segment, and the square forming the new top of the lower segment. They should be the same size, but i

Horizontally. The square forming the new base of the upper segment, and the square forming the new top of the lower segment. They should be the same size, but if they were the Pyramid couldn't taper smaller and smaller towards the top, so the lower face needs to be a few 'elements' more diminutive. .. of course it would depend if you cut it in half between two stone layers, or half way through one stone layer, and if your cut lined up with the top or bottom of the kings chamber or not.