The 19 km of pisé (rammed-earth) walls that enclose the medina were begun under the Almoravids in the 1120s and have been continually patched, raised, and repaired ever since — the colour you see at sunset, the ochre that gives Marrakesh its nickname Red City, comes from the iron oxide in the local clay. There are twenty surviving gates, several of which are themselves significant monuments (Bab Doukkala, Bab Agnaou).
A horse-drawn calèche ride around the full circuit of the walls is one of the standard tourist excursions, and not as cheesy as it sounds — agree the fare in advance.