In watchmaking, the term «architecture» is not a metaphor: it describes how a movement is constructed in structural terms, namely where components rest, how axes are supported, and how space is distributed between the mainplate and bridges. I've disassembled enough calibers to know that two movements with the same complication can be completely different in the way that complication is held together.
The fundamental distinction starts with the mainplate. In classical Swiss construction, bridges cover distinct sectors of the mechanism: one bridge for the barrel, one for the gear train, one for the escapement. In three-quarter mainplate construction, introduced by Ferdinand Adolph Lange in 1864 at Glashütte, a single lamina covers almost the entire movement, leaving only the balance wheel sector exposed. It allows you to see the swan-neck regulator and surface finishing without any disassembly. It remains today the visual signature of traditional German watchmaking.
Another family is that of pillar movements: vertical metal columns that support the mainplate and bridges by spacing them apart, as in the large pocket watch movements of the 19th century. Some contemporary calibers have revived this geometry, partly for aesthetic reasons, making the pillars visible through open dials.
Cantilevered bridges—called «flying» when applied to the tourbillon—eliminate the upper support of the cage. The tourbillon «flies» anchored from one side only. Girard-Perregaux took this logic to three gold bridges that traverse the movement diagonally: a structural element that becomes legible even to those who don't know how to disassemble a caliber. The same principle, with different results, is found in the Ulysse Nardin Freak's flying carousel, where the entire gear train platform rotates in one hour without an upper bridge.
Modular architecture is a special case. The caliber 11—the first automatic chronograph—mounted a Dubois-Depraz module above a Büren base. An industrially efficient solution, mechanically thicker. Today many chronograph calibers still work this way. It's not a shortcut: it's a construction choice with precise advantages in maintainability and production flexibility.
The term also extends to the case. The tonneau construction of the Overseas—barrel base, circular plinth, hexagonal bezel overlaid—is architecture in the fullest sense: functional layers that define both form and structural resistance. Same for layered cushion cases, where geometry is not merely aesthetic but determines how the case absorbs impacts. When a manufacturer talks about «architecture», it's worth asking what supports what.