Walk into a Gothic cathedral and the hierarchy is legible before you've processed a single detail: the nave is taller than the aisles, the crossing is taller still, the choir draws the eye down a long axis toward the altar. No signage explains that the altar matters most. The proportions of the room make the argument on their own, through scale relationships a visitor reads instinctively rather than consciously.
Scale as the first language
Before colour, before ornament, before any symbolic content, relative size is the fastest hierarchy signal a space or a page has available. A cathedral's nave-to-altar scale jump and a webpage's h1-to-body-text scale jump are doing identical work: establishing, wordlessly, what the visitor should register first, second, and last. Get the scale relationships wrong and no amount of colour or labelling fully recovers the hierarchy.
Axis as emphasis
Cathedrals reinforce scale with axis — a single dominant sightline down the nave that architecture bends every other element to support. Pages do the same with a primary reading path, usually top to bottom, left to right in most Western layouts, and the strongest ones bend secondary content to support that path rather than compete with it. A page with six equally emphasised elements has the informational hierarchy of a cathedral with six equally tall naves: technically a building, structurally an argument for nothing in particular.
Hierarchy communicated through scale and axis survives translation into any language. Hierarchy communicated through labels does not.
The best compliment either a cathedral or a homepage can receive is that a first-time visitor knew exactly where to look, and couldn't quite explain how they knew.