accents in Russian

Hello all,

I've just returned from a wonderful holiday in Russia, during which I
visited a lot of churches.

I was surprised to see accents (both acute and grave) on the texts
written on the frescoes of the churches. Were accents formerly in use
in Russian and got lost with time? Or is it a church-specific use (I
suspect the latter since I never saw any accents on monuments or civil
buildings).

Cheers,

Gianni Vacca