What's the lore...

[Waedawen]

The big, over-arching ones were founded by the Combine Empire -- you can find their more detailed ruins on Kunark and Antonica. From there, I can only guess that the small pyramid-like one were built by future wizards with handed-down magic. The architecture style of the pyramid-spires is similar to the Lost Valley in dreadlands, so it may also just be the Combine Empire in a less-elegant building style.