I've been reading about the intuition behind calculating the volume of a pyramid by dividing the unit cube into 6 equal pyramids with lines from the center of the cube and it makes sense since all pyramids are the exact copies of each other and I'm curious how this intuition expands to rectangular prisms. Once we know the formula to calculate the volume of a pyramid we can actually see that lines from the center of the prism indeed divides the shape into 6 pyramids with equal volumes, but without knowing the formula is it possible to somehow say that?
Same question goes for other pyramids with unequal side lengths. How can you say that pyramids with same base and height have equal volumes without knowing the formula?
I'm specifically asking for a primitive method without the use of calculus or other advanced methods because I've been curious about whether or not Egyptians had a way to show it or they just got lucky, or maybe they were only interested with pyramids cut from the unit cube and not the others?