Eight kilometers from the modern town of Ma'rib, where the Wadi Dhana comes out of the hills into the desert plain, the northern end of the ancient dam still stands. It is a ruin of cut stone and carved channels, but it is a ruin of an engineering marvel. The Sabaeans, who ruled this part of southern Arabia from the first millennium BC, built a great earthen dam across the wadi to catch the seasonal floods, and at either end they placed sluice structures of finely worked stone to let the water out into canals.
On the northern bank you find the sluice gate and spillway, built of large blocks fitted with great care, and inscriptions in the Sabaean script that record repairs and the names of rulers who carried them out. The channels once fed a wide network of fields, and the oasis around Ma'rib was famous for its fertility and for the frankincense and myrrh that passed through it on the way north. The Qur'an alludes to the story of the dam's collapse, the flood of the Arim, which tradition places in the sixth century AD and which scattered the people of Saba across Arabia.
The surroundings are stark and beautiful. Dark hills rise on both sides of the wadi, the sky is hard blue and the ground between the stones is pale. In the early morning the light is warm on the masonry, and the valley is silent apart from the wind. It is easy to imagine the water roaring through the gate, and the farmland beyond.
An honest word is needed about travel. Yemen has been at war since 2014, and Ma'rib governorate has been a front line, with fighting, mines and air strikes. Foreign governments advise against all travel there, and this is not a place where anyone should plan to ride. These notes describe a place of history, and the situation on the ground should be checked with reliable current sources before any thought of visiting.
In peaceful times the road from Sana'a, about a hundred and thirty kilometers west, crossed desert and mountains, and Ma'rib offered fuel, simple food and a place to sleep. The dam itself is a short drive from town, and a morning is enough to see it.