Abstract: A container assembly for rapid erection of portable buildings meets the following requirements: it is transportable by a single truck tractor, has dimensions which are customary and permissible for highway transport, and may be quickly erected on-site by simple means, whereby its floor space in the use mode is multiplied over that in the transporting mode and comprises two side containers swingably linked to a central container on the two longitudinal sides of the central container, whereby said side containers swing inwardly to fit one into the other and over the central container. When the assembly is in the swung-in transporting and storing position the available floor space is reduced to approximately one-third of that in the swung-out use position. The container assembly is particularly advantageous for use as a mobile hospital.