A modular self-contained gate for selectively blocking an entryway comprising an ISO standard shipping container modified such that an existing closed end wall of the shipping container comprises an elongate slot-like opening arranged vertically and adjacent an edge of the closed end wall, a substantially flat and rectangular gate comprising a long edge having a length substantially the same as a length of the shipping container and a height less than a height of the opening, the gate aligned with and linearly displaceable through the opening between a first position wherein the gate is stored inside the shipping container and the entryway is open and a second position wherein the gate is extended outside of the shipping container and passage via the entryway is barred, and a support mechanism inside the shipping container suspending the gate such that the gate remains suspended above the ground.