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This monochrome architectural illustration displays a detailed cross-sectional diagram of an ancient Roman hypocausis or underground central heating structure discovered in Paris, France. The technical drawing highlights rows of short, square-profiled masonry or brick supporting pillars, known as pilae stacks, which are arranged neatly across a lower stone foundation to elevate the main flooring of a heated room or bath chamber. By lifting the upper living surfaces, this advanced engineering setup created an open underfloor cavity that permitted warm air, smoke, and radiant thermal energy generated by an external furnace to circulate freely, simultaneously warming the floors and ascending through hollow interior walls via clay flues. This archaeological specimen of classical Roman thermal utility and civil infrastructure, uncovered during historical urban excavations near Notre-Dame in France, belongs to a residential or municipal bath network originally constructed during the 2nd century.