Romex embedded in 1/2 inch of plaster.
Here in Austria that would be an acceptable wiring method, though no one would do that in a plaster & lathe ceiling since it'd be much easier to fish the wires parallel to the joists. One small hole where the wire enters the ceiling and one at the fixture, viola! Done that many times (though I _always_ used flexible pvc conduit). Removed loads of such wiring from our walls here. Old time geniuses here used THHN instead of NM in order to bury it in plaster! _That_ is scary!
