How steep a road could a horse/horse-and-cart travel?

I'm in the early stages of designing a city, and would like some advice about to structure its roads realistically for transport.

The city is circular, with large roads entering the city at north/south/east/west. It should also be on higher ground - doesn't have to crown a mountain, but should be higher than the rest of the immediate countryside.

Given that:

(a) the world uses medieval technology;

(b) horses/horse-and-cart are the most sensible long distance transport;

(c) the roads are straight;

and (d) there is no magic,

HOW STEEP CAN THESE MAIN ROADS BE?

If I can't sensibly have straight roads and an impressive-enough gradient, then I'll redesign the city with a different design. Still, it'd be nice to go along with my current mental image!

Further contextual information:

The city is divided into concentric rings, with the palace at the centre and the poorest at the outskirts. A significant slope would therefore make the palace even more impressive to viewers.

The city evolved from a simple trading town at a set of crossroads, but developed in importance and resources. The straight roads are a remnant of that past - while they're not the best defensively, internal walls divide class districts, and are each equipped with defences. (Being on higher ground also helps for defence).

The area may have once been volcanic - the city is fed by natural springs, and may explain a hilly/mountainous terrain.

I've also had a look here for info about road-building, but it didn't seem to cover this.

posted about 7 years ago

K. Price‭

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