Definition of "revetting"

A 200-ton rockfall recently blocked the Machynlleth sidings, trapping several locomotives; a rock-slip on the approach embankment to Talerddig required expensive revetting last year; and on the coastal section to Barmouth an 80 foot-high stone revetment was completed some time ago at Friog; [...].

1964 December, Mark Bourne, “The rejuvenation of the Cambrian line”, in Modern Railways, page 390