The Great Marib Dam is the most famous ancient ruin in Yemen. Located 8 km south-west of the city of Marib, between the northern and central Balaq mountains, it collected water flowing from the eastern highlands and irrigated an estimated 70 square kilometres of the Marib valley -- one of the largest ancient irrigation systems in the world.
The dam was 35 metres high, 720 metres long, and 60 metres wide at the foundations, built from massive stone blocks faced with rough volcanic stone. Two sluice openings (Al-Sadafain) channelled water into the irrigation network; their walls still stand as described by the 10th-century geographer Al-Hamdani. Construction dates to approximately 750 BCE under the Sabean ruler Yatha' Amar Watta I, though the structure was expanded and repaired over many centuries. The dam's final failure around 570 CE contributed to the collapse of the Sabean kingdom and is referenced in the Quran as the Flood of the Dam.
The site was damaged in air strikes during the civil war.