abatis
advanced work
arch dam
backstop
balistraria
balustrade
bamboo curtain
bank
banquette
bar
barbed-wire entanglement
barbican
bare
barrage
barricade
bartizan
bastion
battlement
bear-trap dam
beaver dam
blank wall
blind alley
blind gut
block
blockade
blockage
bolt
boom
bottleneck
boundary
brattice
breakwater
breastwork
brick wall
buffer
buffer state
bulkhead
bulwark
bumper
casemate
cecum
chain
cheval-de-frise
choking
choking off
circumvallation
clog
circle
cover
environment
fence
frame
layer
mass
obstacle
rampart
requirement
resistance
ridge
screen
shield
sphere
structure
tower
wall
Carrier
carrier
charrier
farrier
ferrier
harrier
merrier
perrier
scarier
terrier