Barking is a borough on the far reaches of east London. Served by the District Line and Hammersmith and City services the station is in Travelcard zone 4. The station was originally part of a larger mainline network that ran along the Thames estuary in Essex to Southend-on-Sea. Barking became the terminus of the Hammersmith and City Line and fully fledged part of the London Underground network after electrification in 1908.