A foot path or pack horse trail up a steep hill was often straight up - shortest distance - but as soon as you put wheels into the equation, you are looking at a zig zag road with shallower gradient.
About ten minutes walk from where I live is a steep section of main road, an incline possibly built as recently as the 1960s, by the look of the retaining walls. This bypasses what I thought was the original zig-zagging road. I only thought the latter was the original road because: 1) the current road uses retaining walls**, so its building involved serious earthworks; 2) I didn't think such a steep section would have been viable before more powerful*** road vehicles appeared.
However, on reading, in the local library, about the history of the village, I saw a mention of a by-pass being built to avoid the original steep road. (This possibly coincided with the building of the Southampton and Dorchester Railway through the area and, soon after, a station****, one that would have attracted more traffic onto the road (and which caused what would have been, at best, farmland, to mutate into a growing settlelment).
** - I'm now guessing that the new retaining walls were built in order to allow the new road to be wider than what was there a couple of centuries ago... and to allow the (safe) building of the houses now looking down on the road from both sides.
*** - I expect the delay in the building of the incline was more to do with planning issues and finance than, say, the power of vehicles in the 40s and 50s.
**** - The station was built to serve Poole, a few miles to the south. Being a port heavily engaged in the transport of goods along the English Channel coast, there was a lot of opposition to a railway entering the town. It was only later that the village station became a junction for a line to Poole and, eventually, Bournemouth (which was later connected to the network more directly from the east). Later still, it became a double junction, becoming the southern end of the Somerset and Dorset (S&D) line (aka the Slow and Dirty).