Sijilmassa was the first independent Arab and Islamic city in Morocco, founded in 757 AD on the edge of the Tafilalt oasis as the northern terminus of the trans-Saharan caravan trade. For half a millennium it was one of the wealthiest cities in the western Islamic world; today it is a five-minute drive west of Rissani and consists mostly of low mud-brick walls, the shell of a 14th-century gate, and a long mosque foundation traced in the dust.
The site is unfenced and free, and a guide is essential to make any sense of what you are looking at — the active archaeological dig of the 1990s has long since wound down and there is almost no signage. The atmosphere is the main draw: the palms, the wind, and the absence of crowds. Come at sunset.