The tight-binding model is considered for a square lattice with filling factor 1/2. The array has the shape of a rectangle with boundary conditions in both directions twisted by and . The components of the twist are associated with two components of the magnetic flux in torus geometry. An analytical expression is obtained for the energy and for the components of the persistent current (PC) at a given flux and temperature. It is shown that at zero temperature the PC density is proportional to the vector potential with a coefficient which does not depend on the size of the system. This happens because the Fermi surface for a square lattice at filling factor 1/2 is flat. Both the energy and the PC are periodic functions of the two flux components with the periods and where , and q and s are integers which depend on the aspect ratio of the rectangle. The magnitude of the PC is the same as for superconductors. Therefore, a 3D system constructed from a macroscopic number of isolated coaxial cylinders at zero temperature is reminiscent of London's superconductor. It exhibits the quantization of trapped flux as well as the Meissner effect. However, all of the phenomena are of a mesoscopic nature. The critical field decays with the effective size of the system, . The magnitude of the PC decays with T as , where t is the hopping amplitude and a is the lattice constant.