Excavations at eastern Africa’s oldest and biggest cemetery offer a new perspective on the reasons why ancient humans built great monuments.

The Lothagam North Pillar Site is a communal cemetery built around 5000 years ago near Lake Turkana, Kenya, by the region’s first herders. At the site there are 1.5-metre-tall stone pillars, nine stone circles and a vast 700 square metre raised platform mound, together with the remains of at least 580 people.

Researchers usually think such large structures were the work of stable, complex, …