A pyramid is a self-supporting structure. Anyone who has dug a hole and tossed the dirt in a pile quickly learns that the pile roughly (and naturally) forms a pyramid shape. Likewise with mountains: Rock and dirt forced upwards due to plate tectonics causes portions of the Earth to become shaped like pyramids. Anything on Mars that looks like a pyramid would more likely be such a natural hill or formation.
If there are any Martians on Mars, then any pyramid they built would only prove lots of Martian manpower and that they are not very technologically sophisticated. Come on, humans built them thousands of years ago with no modern equipment.
The theory that aliens built something that could only be discovered by humans as they advanced (which is straight out of
2001: A Space Odyssey) would much better be something along the lines of a radio beacon set up by aliens. Animals can pile stuff into a pyramid shape (ever seen an ant hill?) But only highly evolved beings can send and receive radio waves. This is why the
SETI project is much better suited to finding any advanced aliens out there.
As for the pyramids here on Earth, I always find the claim that the people of that time couldn't build them, and thus must have help from aliens, not only insulting to the human race, but possibly slightly bigoted towards the dark-skinned Egyptians. As mentioned, given enough manpower (which ancient Egypt clearly had) anyone can build a self supporting structure. But notice how no one ever claims that the white skinned ancient Greeks could never have built things like the Colosseum or the Parthenon and that they must have had alien help. Just think about the Parthenon built around 448-432 BC: Twenty-two thousands tons of solid white Pentelic marble went into its construction! And just like the ancient Egyptians, the ancient Greeks also had no modern equipment when they built it. Yet they built this incredible structure, complete with monestrous marble columns, which were built to take advantage of known optical illusions so that the columns would appear perfectly straight and evenly spaced (even though they weren't.)
Thus it appears that the ancient Greeks were far superior than any Martians!
