this is assumed to be the eastern side on Cornhill, with the Saxons based on the higher status western Ludgate Hill. Impact of London's Wall London's defensive wall seems to have had an unintended impact on the river, acting like a dam to impede the flow of the river and create the marshy conditions which characterised the open space at Moorfields. The wall's surrounding ditch may have diverted some of the water that would otherwise have gone through the City. Walbrook skulls In 1838 construction workers building a new sewer under Blomfield Street, on the course of the Walbrook, discovered very large numbers of human skulls, though very few other bones were present. Since that time around 300 further heads have been found in the bed of the river, generally in the vicinity of the initial discovery. It is believed that the number of heads destroyed by development, or awaiting discovery may be in the order of many thousands. Writing around 1136, Geoffrey of Monmouth seemed to be aware of the presence of the remarkable number of skulls on the riverbed. His History of the Kings of Britain explained their origin as resulting from a massacre occurring during a Roman civil war, the Carausian Revolt of AD 286–296. In Geoffrey's account, a Roman legion under Livius Gallus, besieged in London, agrees to surrender to the forces of Julius Asclepiodotus on condition they are given safe passage out of Britain. Asclepiodotus is happy to grant this, but his allies the Venedoti moved on the captives, beheading them all in a single day. Geoffrey wrote that the river was afterwards named after Livius Gallus, the leader of the beheaded Romans, as Nantgallum in Welsh (the language of the native Britons), or in the Saxon English as Galobroc, from which Walbrook was derived. However, Geoffrey's History is unreliable, and other theories have been proposed. Some historians consider these skulls to be a result of the rebellion of Boudica. More recently, the skulls have been dated mostly to the early 2nd century AD, and it has again been suggested that the skulls are the consequence of an anti-Roman rebellion in the 120s when London suffered a second major fire often called the Hadrianic fire. The three martial explanations may link to the proposition, made by archaeologists, that the skulls represented ritual deposits of heads related to the Celtic cult of the head. Excavations in