If we want more stable 'staffs' stone is a good choice. And two pillars makes us think about twins. To secure the meaning of twins another stone is placed on top, a lintel stone. We have a trilithon like the one on Tongatapu, with solstice signs on top. That such 'trilithons' earlier were made by wood may be inferred from the indigenous religion of Japan, Shinto, which has a sacred sign not shaped like a cross but as a portal or door (torii/mon):

This picture of Itsukushima Shrine from a local Hiroshima broschure illustrates that there really should be not only a lintel but also other beams to stabilize.The sign of dokana I think.