In 1969, I made my first few tentative steps into the African bush, beating it with a stick to drive away the snakes. Within two hundred yards, I came across a low ditch and bank: little did I realise then that this was part of the World's longest ancient earthworks - one of the largest archaeological phenomenon on this planet!

Many years later, I was surveying these earthworks at a rate of about two hundred miles a month. My orienteering tracksuit was constantly being torn by the thorny undergrowth and sewn back together each night by my wife. A grand zonation pattern began to emerge, with small inner enclosures within a core zone; and much larger enclosures on the perhiphery. Through my surveys, I was now watching past migratory wave fronts rolling across the landscape centuries before the emergence of the Benin dynasty.

Aware that Peter Lloyd had discovered and partly mapped Sungbo's Eredo around Ijebu-Ode, over a hundred miles west of Benin, I ventured into the Yoruba rainforest too. Here, the great 100 mile long ditch had been dug vertically making a twenty metre high rampart through the forest. The feature remained spectacular because the clay, silt and iron-oxides in the soil combined to make a hard lateritic crust on exposure to air. Sungbo's Eredo has been dated to the early C9th AD, with deepening about 300 years later; so making it the earliest proof that kingdom formation occurred in the African rainforest as in the savannah.

Back in Benin, as I talked to old men and women, I drew up a picture of the forest ditches as defence against elephants, against enemies, against the ever-threatening spirit world, and acting as community land boundaries cneturies before the early C14th Benin Kingdom avbiogbe began demarcating its boundaries with trees. The cultural landscape became full of meaning, augmenting what I was reconstructing of the history. This, and so much other neglected, vulnerable mud archaeology in Nigeria destroyed my career ... but made my life.

As fallow periods shorten, cities expand and bulldozers wreck havoc, these extensive earthworks are beginning to disappear. Some can still be seen on the recent (2008) high-resolution Googlemap imagery strips but, unless you know the land, they can be easily confused with other linear features. More of the world's archaeologists need to go to Nigeria: Nigeria has the greatest linguistic and ethnic diversity of any country and it deserves to be better studied.