algae
ancient
artillery
artillery piece
blue
cannon
castle
citadel
coastal
coastal defence
coastal defences
defence
defensive
engraving
firearm
grain
gun
iron
masonry
metal
military
mortar
ocean
old
ornate
parapet
ripples
sea
shadows
slabs
steel
stone
stonework
stronghold
wall
war
warfare
water
waves
wood
wooden
woodgrain