Short answers, pulled from the story.
The City of London was established by Roman legions around AD 43 as Londinium. A bridge across the Thames was built as early as AD 50, turning the settlement into a major port and road hub for Roman Britain.
The City of London covers just 1.12 square miles, making it the smallest city in the United Kingdom by area. Its 2021 census population was 8,583 residents, though over 500,000 people were employed there as of 2019.
The City of London was never reformed by the Municipal Corporations Act 1835 because it already had a broader electoral franchise than that law required. Today most of its voters are business representatives rather than residents, a system expanded by the City of London (Ward Elections) Act 2002, which doubled the non-resident business franchise from roughly 16,000 to 32,000 voters.
The City of London vies with New York's Lower Manhattan as the world's leading financial centre. In 2009, London's foreign exchange market handled around $1.85 trillion of the $3.98 trillion global daily turnover, representing about 46.7% of all trading. The Bank of England, the London Stock Exchange, and Lloyd's of London are all based there.
The City suffered heavy aerial bombing during the Blitz. Raids in late December 1940 caused a firestorm known as the Second Great Fire of London, destroying large parts of the historic fabric. St Paul's Cathedral survived. Rebuilding in the following decades, including the Barbican Estate constructed between 1965 and 1976, dramatically altered those damaged areas.
22 Bishopsgate, completed in 2020 and designed by PLP Architecture, is the tallest building in the City at 278 metres and 62 floors. St Paul's Cathedral, completed in 1710, was the tallest structure in the City for 257 years until CityPoint overtook it in 1967.