The invention relates to a modular system for building stadiums or bleachers, comprising a support structure, benches, paths for the spectators, technical modules and stairs. The support structure is designed as a framework, the individual parts of which are detachably connected to each other at the node points. All individual parts of the modular system are dimensioned in such a way that said individual parts fit in an ISO container. The technical modules and stairs are accommodated in an ISO container.