badbi'u lujvo

bi1=ba1 is a rampart/[protective wall] protecting bi4=ba2 from threat/peril/potential ba3 (event).

Cf. bandu, bitmu, badydi'u.

In notes:

badydi'u
b1=d1 is a defensive building (castle, fortress etc.) for protection of b2 from b3 (enemies, danger).
mradi'u
d1=m1 is a castle/fortress/fort/citadel [defensive building/edifice] for protecting/sheltering m2 from danger/threat m3.