You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Plymouth

Context:
Throughout the 17th century Plymouth had gradually lost its pre-eminence as a trading port. By the mid-17th century commodities manufactured elsewhere in England cost too much to transport to Plymouth and the city had no means of processing sugar or tobacco imports, although it did play a relatively small part in the Atlantic slave trade during the early 18th century.

Question:
In what century did Plymouth cease to be a vital trading port?

17th