So you need to Pick a problem: hang a road across a strait

The water is far too deep for piers, and a plain beam this long would sag and snap.

1. So you build two tall towers and drape cables over them, cliff to cliff. The cables carry the weight in tension, and the towers carry it straight down.
2. But a cable that thick is far too heavy to lift.
3. So you spin it in place, one wire across and back, thousands of times.
4. But the cables pull on their ends with enormous force.
5. So each end is tied into an anchorage, a massive block of concrete locked into the rock.
6. But wind: in 1940 a steady wind twisted the thin Tacoma Narrows deck until it tore itself apart.
7. So modern decks are stiff, with deep steel trusses or streamlined box girders.

Two towers, two anchorages, and thousands of wires pulled tight.