@slowwalker,
Once in a movie I could see this type of gate! But it was at China! I think both countries has the belief of "Geumgang gate". In Sri Lanka, I have never found this gate before! I think it's the guardian of temple and the teaching! Like a castle got it's main gate, these temples are guarded by those powerful spirits!
It's great to see you visit them and made a great article with wonderful photography collection!

Cheers~