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Monolith is an application built from a simple codebase that scales vertically. They form as part of the standard set of commonly used architectural patterns e.g. Model-View-controller. Monoliths are a really good way of starting projects. They have a tightly coupled architecture, how tightly coupled depends on team size and experience. Monolithic products successfully scale to be really large by increasing hardware and by evolving their design into N-Tier and then onwards, often becoming a subsystems architecture model.