"Africa's Great Green Wall"

Before and after images source: "Africa's Great Green Wall," Celcias

The Community of Sahel-Saharan States (CEN-SAD) has initiated a project to build a Great Green Wall across the continent from Mauritania in West Africa to Djibouti in the East. The project is an attempt to stop growing desertification in the northern regions of the continent. A 5 km wide 7,000 km long green strip of trees is to be planted across the desert from Dakar to Djibouti to constitute a barrier to further progress of desertification.

Read more at Global Envision.

This is an extremely ambitious project, and one that has not yet been completely funded. There is at least one precedent. The Great Hedge of India was installed in the 19th century to help stop smuggling (of drugs). It stretched a distance of 2,300 miles and was guarded by nearly 12,000 men.