What Was The Second Largest City In England In The Late Middle Ages?

Norwich.

Which prospered because of the wool trade.  Although we think of East Anglia as a largely agricultural region now, in medieval times it was most famous and wealthy for sheep.  The west Norfolk sheep breeds had long coats, the long fibres of which were suited for fashioning into what became known as worsted wool (after the Norfolk village of Worstead).  Nowadays, worsted wool is made all over the world.

Norwich itself became the principle marketing centre of one of the most wealthy and densely populated parts of England. Textile production in the city continued to be important until the mid 1800s.

The entire county of Norfolk prospered from the wool trade.  For instance, in 1150 Thetford was the 7th largest town in England and by 1200 King's Lynn was the probably the 5th largest port.

The economy of the region changed greatly with increasing trade with the New World, and later with the far East, from about 1600.  Drainage of the salt marshes also made East Anglia more suitable as agricultural land, growing much needed food for the swelling population in the Industrial Revolution.

Norwich