During the 19th century, London grew enormously to become a global city of immense importance. It was the largest city in the world from about 1825, the world's largest port, and the heart of international finance and trade. Railways connecting London to the rest of Britain, as well as the London Underground, were built, as were roads, a modern sewer system and many famous sites. Overview During the 19th century, London was transformed into the world's largest city and capital of the British Empire. The population rose from over 1 million in 1801 to 5.567 million in 1891. In 1897, the population of Greater London was estimated at 6.292 million people. By the 1860s it was larger by one quarter than the world's second most populous city, Beijing, two-thirds larger than Paris, and five times larger than New York City. At the beginning of the 19th century, the urban core of London was contained to the west by Park Lane and Hyde Park, by Marylebone Road to the north, along the south bank of the Thames at Southwark, and to the east as far as Bethnal Green and Spitalfields. At the beginning of the century, Hyde Park Corner was considered the western entrance to London; a turnpike gate was in operation there until 1825. With the population growing at an exponential rate, so too did the territory of London expand significantly: the city encompassed 122 square miles in 1851 and had grown to 693 square miles by 1896. During this period, London became a global political, financial, and trading capital. While the city grew wealthy as Britain's holdings expanded, 19th century London was also a city of poverty, where millions lived in overcrowded and unsanitary slums. Life for the poor was immortalized by Charles Dickens in such novels as Oliver Twist. One of the most famous events of 19th century London was the Great Exhibition of 1851. Held at The Crystal Palace, the fair attracted visitors from across the world and displayed Britain at the height of its imperial dominance. Immigrants As the capital of a massive empire, London became a draw for immigrants from the colonies and poorer parts of Europe. A large Irish population settled in the city during the Victorian era, with many of the newcomers refugees from the Great Famine (1845–1849). At one point, Irish immigrants made up about 20% of London's population. In 1853 the