On the morning of Friday, December 5, 1952, with the temperature just below freezing, a dense fog settled over Greater London. The fog was notable for its density, its duration, and almost complete absence of remission in either density or temperature for four long days. The fog was generally considered to be the worst in living memory. The fog had far-reaching effects on city life. Low visibility contributed to numerous traffic accidents. Emergency services were taxed both by increased demand and poor driving conditions. Ambulance services were kept busy by an apparent increase in people suffering from a variety of illnesses, predominantly respiratory. At the annual Smithfield Show, featuring prized pigs, cows, sheep, and goats, a number of cows died. London is situated in the valley of the River Thames in southeast England, bounded on the north and south by chalk hills. Greater London covers 720 square miles and is inhabited by 8 million people.