English: Brent Cross: Northern Line viaduct over the A406 North Circular Road The viaduct was completed in 1924 to carry the then Charing Cross, Euston and Hampstead Railway's extension to Hendon over the valley of the River Brent. The line was subsequently extended to Edgware and was subsumed into London Undeground's Northern Line. The far arch on the left is one through which the river flows. Looking at old Ordnance Survey maps of the area the railway is conspicuously entirely missing from the 1938 Edition leaving just a blank white swathe through the detail of the housing estates. Was this a security precaution to camouflage a bombing target in view of the impending hostilities of the Second World War? The slip road coming up from the North Circular leads to the A41 and Brent Cross, while a speed camera is just visible by the right side of the right hand arch to reinforce the 40mph limit on the road.