Simplify the following text for a Grade 9 native English-speaking person.
Original: The city was a center of the British East India Company 's opium trade during the 18th and 19th century ; locally produced opium was sold at auction in Kolkata , to be shipped to China .
Simplified: The city was a center of the British East India Company 's opium trade during the late 18th and 19th century .