The technical bases of Gothic architecture -- Gothic spaciousness -- The early Gothic grid -- A first Gothic system, ca. 1160-1180 -- Late 12th-Century changes -- The flying buttress and the second Gothic system -- After Chartres and Bourges: diffusion and changes between 1200 and 1230 -- Divergent trends in the early 13th century -- A third Gothic system: the Rayonnant style -- Late 13th-Century architecture