London

London is the capital city of the United Kingdom.

A big river called the Thames flows through it. London is very old. It has castles, palaces and famous bridges. Millions of people live there.

London is the capital of the United Kingdom and by far its largest city. It lies in southeastern England, on both banks of the River Thames, about 80 kilometers upstream from where the river meets the North Sea. About 8.8 million people lived in Greater London at the 2021 census.

London is one of the oldest of the world's great cities: its history goes back almost 2,000 years, to a town the Romans built called Londinium. Today it is the center of the country's business, transportation and culture, and people from all over the world live there.

London lies astride the Thames about 80 km upstream from its estuary on the North Sea. Britannica calls it among the oldest of the world's great cities, with nearly two millennia of history, one of the most cosmopolitan, and by far Britain's largest metropolis and its economic, transportation and cultural center.

Greater London, a metropolitan county formed in 1965, covers 1,572 km² and counted 8,799,728 people at the 2021 census. Seen from space, it sits compactly inside a Green Belt of open land, ringed by the M25 motorway at a radius of about 30 km from the center; strict planning controls halted the growth of the built-up area in the mid-1950s. At its heart is the City of London, a corporation of just 2.8 km², often called the Square Mile.

London has many famous places.

The Tower of London is an old castle by the river. Big Ben is a giant bell in a tall clock tower. Tower Bridge can lift up its road to let ships pass.

The Tower of London is a fortress built around the White Tower, which William the Conqueror put up beside the Thames more than 900 years ago. Upriver, the Palace of Westminster is where Parliament meets, and next to it stands Westminster Abbey, where kings and queens have been crowned since the 1000s.

Big Ben is the nickname of the Great Bell in the palace's clock tower, the Elizabeth Tower, which is 96 meters tall. Tower Bridge, finished in 1894, is a drawbridge: its two halves of road lift up so tall ships can pass. After the Great Fire of 1666, Christopher Wren designed a new St. Paul's Cathedral.

Several UNESCO World Heritage Sites are in London. The Tower of London (1988) grew around the White Tower, a massive Norman keep that William the Conqueror built on the Thames to protect London and assert his power. Westminster (1987) combines the Palace of Westminster, rebuilt from 1840 in neo-Gothic style on important medieval remains, with St. Margaret's Church and Westminster Abbey, where every sovereign since the 11th century has been crowned. Maritime Greenwich (1997) includes Wren's Royal Naval College and the Old Royal Observatory, and the Royal Botanic Gardens at Kew (2003) have studied plant diversity since 1759.

The 13.7-tonne Great Bell called Big Ben hangs in the 96 m Elizabeth Tower. Tower Bridge, a double-leaf bascule bridge completed in 1894, has twin towers 61 m above the river; its leaves are now raised about 800 times a year, against more than 6,000 in 1894. After the Great Fire, Sir Christopher Wren designed a new St. Paul's Cathedral and about 50 rebuilt churches.

London is often mild.

Winters are cool but not very cold. Summers are warm but not very hot. It can rain in any month. Snow does not come often, and it usually melts fast.

London has mild winters and warm, but not hot, summers. The average temperature is about 5.5 °C in January and 18 °C in July. About 585 millimeters of rain and snow fall in a year, spread evenly over all 12 months, and an average year has about 200 dry days.

Sleet or snow falls on about 20 days in an average year, mostly from January to March, and it rarely piles up. The center of the city is usually warmer than the countryside around it, because buildings, traffic and heating give off heat. This is called a heat island.

Weather records for London go back to 1659. Modern London has the equable climate of southeastern England: an average daytime temperature of 11 °C, 5.5 °C in January and 18 °C in July, with the sun appearing on five days out of six. Precipitation of about 585 mm is spread evenly through the year, and sleet or snow averages about 20 days a year but varies greatly; the snowiest winter on record, 1695, had snow on 70 days.

The city forms a heat island: minimum temperatures average 1.9 °C higher than the surrounding country and can be 9 °C higher on single nights. Coal smoke once caused the notorious smogs, until the Clean Air Acts of 1956 and 1968 banned burning coal; traffic pollution remains a problem. Cleaner water has brought salmon, sea trout and even sea horses back to the tidal Thames, and the Thames Barrier's 10 movable gates can be swung up to seal London off from the sea at times of flood risk.

People from many countries live in London.

Some families have lived there a long time. Others came from far away. London has big green parks. At one huge garden, scientists study plants.

About 8.8 million people lived in Greater London in 2021. London's population has gone up and down: 5.6 million people in 1891, about 8.6 million by the start of World War II, then down to about 6.6 million in the 1980s as many families moved out of town, and up again since.

Britannica calls London one of the world's most cosmopolitan cities, because people from many countries have made their homes there. Green spaces stretch from Hyde Park and Kensington Gardens in the center out to Richmond Park, and at Kew Gardens scientists have studied plants since 1759.

Britannica describes London's layout as rings. At the center is the City of London, the 2.8 km² historic core. Around it lies Inner London, built up from the late 18th century until World War I, with terraced houses and, where World War II bombs or postwar clearance struck, denser council housing. Outer London is mostly semidetached homes from a building boom of 1925–39, and the Metropolitan Green Belt makes the final ring.

The population grew from 5.6 million in 1891 by about 3 million to its peak at the outbreak of World War II, then fell by about 2 million to some 6.6 million in the mid-1980s as people and firms moved out for space; the 2021 census counted 8,799,728. A chain of green spaces runs through Hyde Park, Kensington Gardens, Battersea Park and Wimbledon Common to Richmond Park, Kew and Hampton Court Park, and the Royal Botanic Gardens at Kew, founded in 1759, became a World Heritage Site in 2003.