Researchers studied an old wall at Oued Beht in north-west Morocco during work in 2023. People built it around 4,000 to 3,500 years ago. It probably helped protect part of a hill beside a river. It is the oldest known large building work of this kind in north Africa outside the Nile Valley.
The builders made a wall, a bank of earth and a ditch across a narrow part of the hill. This work needed planning and many workers. Researchers do not know exactly what danger people faced. They think people probably competed for land, useful materials and control of routes through the area.
People also used Oued Beht much earlier, around 5,400 to 4,900 years ago. They grew wheat and barley, kept farm animals and made tools and pots. Researchers are not sure if people lived there all year. The later wall adds to evidence of links between north-west Africa and other places around the Mediterranean Sea.
People returned to the hill between the 11th and 13th centuries. They rebuilt the wall and started a small village or farm nearby. They also buried people in an area between the two places.
