Before Holborn Viaduct closed, a new line between and the tunnel was constructed on a different alignment slightly to the east and at a lower elevation, providing the opportunity to build of office space above the station on a site. City Thameslink was built to replace Holborn Viaduct station. The total cost was estimated at between £360 and £450 million. Because of a proposed routing for the second phase of the Jubilee line through the area, part of the station was built to allow for a future interchange.