It passes St Catherine's Hill, an Iron Age hill fort and some plague pits, which were common graves for victims of the 1666 plague. It then passes under the former Didcot, Newbury and Southampton Railway, whose line from Winchester to Shawford Junction was operational between 1891 and 1966, before being diverted through a culvert under junction 11 of the M3 motorway. Originally this was the site of a bridge which carried the road from Winchester to Botley, but this was replaced by a full headroom concrete tunnel in the late 1930s, when the junction between that road and the new Winchester Bypass was built over the navigation. When the M3 motorway was constructed, following almost the same line as the bypass where it crossed the navigation, the tunnel was reduced to a culvert, although the original plans for the motorway would have destroyed most of the top pound. The building of the M3 across Twyford Down, a small area of ancient chalk downland, was controversial at the time, but the removal of the Winchester Bypass which ran to the west of St Catherine's Hill close to the navigation and its conversion back to grassland has brought tranquility back to the valley. The canal is on the western edge of Twyford Down, and continues through Twyford Lane End Lock before it briefly rejoins the river. Some south of the junction are Tumbling Bay Hatches, originally used to control levels in the water meadows to the east of the river. A modern sluice was installed just to the north of the 19th century hatches in 1971, and controls flow to the Twyford Drain, the main channel to the east of the navigation, which follows the river channel almost to Shawford Bridge. Modern maps, however, label the drain as the River Itchen.