To avoid the need to purchase agreements for running under surface buildings, the tunnels were bored below roadways, where construction could be carried out without charge. At the northern end of the railway, the need to pass deep beneath the bed of the River Thames and the medieval street pattern of the City of London constrained the arrangement of the tunnels on the approach to King William Street station. Because of the proximity of the station to the river, steeply inclined tunnels were required to the west of the station. Because of the narrow street under which they ran, they were bored one above the other rather than side by side as elsewhere. The outbound tunnel was the lower and steeper of the two. The tunnels converged immediately before the station, which was in one large tunnel and comprised a single track with a platform on each side. The other terminus at Stockwell was also constructed in a single tunnel but with tracks on each side of a central platform.