Simplify the following text for a Grade 8 native English-speaking person.
Original: In the 11th and 12th century Soest grew considerably , making it one of the biggest towns in Westphalia with some 10,000 citizens .
Simplified: In the 11th and 12th century Soest grew a lot , making it one of the biggest cities in Westphalia with some 10,000 citizens .