Question: What company built a railway line that runs along the boundary between Hertfordshire and Essex for much of its length?

Context paragraphs:
Northern and Eastern Railway: The Northern & Eastern Railway (N&ER) was the British railway company that built what is now the West Anglia Main Line, one of the two main lines of the Great Eastern Railway, the other being the Liverpool Street -to-Norwich line built by the Eastern Counties and Eastern Union Railways.  The N&ER and Eastern Counties Railway merged in 1844.

Watarase Keikoku Line: The Watarase Keikoku Line (わたらせ渓谷線 , -sen ) is a Japanese railway line connecting Kiryū Station in Kiryū, Gunma and Matō Station in Nikkō, Tochigi.  This is the only railway line that the third-sector company Watarase Keikoku Railway (わたらせ渓谷鐵道 , Watarase Keikoku Tetsudō ) operates.  The company and line are also known as "Watakei" (わた渓 ) or "Watetsu" (わ鐵 ) .  The company acquired the line from the East Japan Railway Company (JR East) in 1989.  As the name suggests, the line runs along the Watarase River through a deep valley.

Central Coast &amp; Newcastle Line: The Central Coast & Newcastle Line is a NSW TrainLink passenger train service that runs along the Main North railway line in New South Wales, connecting the state's two largest cities, Sydney and Newcastle.  The service runs from through to on the Main North railway line to on the partly-closed Newcastle railway line, and services the Hawkesbury River region, the Central Coast and the city of Newcastle.

Carlingford railway line: The Carlingford railway line is a minor railway line in Sydney, Australia.  Opened in 1888, the line runs north-south between the suburb of Carlingford and the Main Suburban railway line at .  Passenger services on the line form part of the Sydney Trains commuter rail network and are marketed as the T6 Carlingford Line.  The railway line's small catchment, low patronage, short platforms and single track for much of its length mean the T6 generally operates as a shuttle service, with passengers changing at Clyde for T1 North Shore, Northern & Western Line services to the Sydney central business district and Parramatta.  Most of the line is planned for conversion to light rail as part of the Parramatta Light Rail network.  As a result, the line will permanently close.

South Coast Line: The South Coast Line is an intercity rail service operated by NSW TrainLink that services the Illawarra region of New South Wales, Australia.  The service runs from , and runs the entire length of the eponymous South Coast railway line to .  The service also runs along the Eastern Suburbs railway line at peak hours and the Port Kembla railway line to .  It is operated with NSW TrainLink H sets and Sydney Trains T sets, with Endeavour railcars operating the service on the non-electrified line between and Bomaderry.

Belgian railway line 130A: The Belgian railway line 130A is a railway line in Belgium connecting Charleroi with the French border near Erquelinnes.  Completed in 1852, the line runs 29.3 km.  It runs along the river Sambre, crossing it several times.  Beyond Erquelinnes, a French railway line continues towards Jeumont, Saint-Quentin and Paris.  Until the opening of the Paris–Brussels–Cologne high-speed lines, international passenger trains between Paris and Cologne traveled along line 130A.

Etsumi-Nan Line: The Etsumi-Nan Line (越美南線 , Etsumi Nansen , "Etsumi South Line") is a railway line in Gifu Prefecture, Japan, operated by the third-sector operator Nagaragawa Railway (長良川鉄道 , Nagaragawa Tetsudō ) .  The line connects Mino-Ōta Station in Minokamo with Hokunō Station in Gujō.  It is the only railway line operated by the Nagaragawa Railway.  The line was originally operated by Japanese National Railways (JNR).  JNR planned to connect the Etsumi-Nan Line and Etsumi-Hoku Line ("Etsumi North Line"), but the plan was never realized.  The north line was later succeeded by West Japan Railway Company (JR West), while the south line was taken by Nagaragawa Railway, a newly founded third-sector company, in 1986.  As the company name suggests, the line runs along Nagara River.  As a consequence of Japan's declining population and frequent natural disasters (such as typhoons and heavy snowfall), the company is facing financial difficulties.

KTM East Coast Railway Line: The East Coast Railway Line is the single track metre gauge runs between Gemas railway station, in Negeri Sembilan and Tumpat railway station, in Kelantan of Malaysia.  Gemas is the rail junction between the West Coast line and East Coast railway line.  Like the West Coast Railway Line, it is called the East Coast Railway Line (Malaysia) because it serves two of Peninsular Malaysia's East Coast states, namely Pahang and Kelantan.  In fact, it does not run along the coast at all and only meets the South China Sea when it terminates in Tumpat railway station.  It runs through the interior, often through deep jungle, thus earning the nickname Jungle Railway.  Terengganu is the only state in Peninsular Malaysia not served by the KTM railway network.

West Anglia Main Line: The West Anglia Main Line is one of the two main lines from , the other being the Great Eastern Main Line to Ipswich and Norwich.  It runs generally north through Cheshunt, Broxbourne, Harlow, Bishop's Stortford and (near Saffron Walden) to Cambridge, with branches serving Stratford, Hertford and Stansted Airport.  The line runs along the boundary between Hertfordshire and Essex for much of its length.

Laupheim–Schwendi railway: The Railway line Laupheim West - Schwendi in Germany connected the town of Laupheim with the then village of Schwendi.  The railway line was opened by the Royal Württemberg State Railways on 17 May 1904.  It branched off from the Württemberg Southern Railway, connecting Ulm with Friedrichshafen.  The length of the railway line was 16 km (approximately 10 miles).  The railway line had the classification number of 4510.  The steam locomotive used on the line, received the nickname "Rottalmolle" by the local population, referring to the course of the railway line through the valley of the river Rot.

Supporting paragraphs: Northern and Eastern Railway West Anglia Main Line
Answer: The Northern & Eastern Railway