Many visitors to London will visit St Paul's Cathedral, so they will spend some time in the City of London, but often their itineraries mean that they don't take the time to explore the rest of this area. The City of London is often referred to as the Square Mile, on account of its size, and its compactness makes it ideal for walking around. It's one of the oldest parts of London. with its history going back nearly 2,000 years to when the Romans arrived. In the course of its history there have been two major events the Great Fire of 1666 and the Blitz, the period of intensive bombing during World War II. Today the City of London is best known for its financial institutions. The City's delights are more subtle and require a bit more effort to discover, but for those who do will be rewarded with a medieval Guildhall, historic City Churches, charming, narrow alleyways and over 150 delightful small parks and open spaces.