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:
The settlement of Plympton, further up the River Plym than the current Plymouth, was also an early trading port, but the river silted up in the early 11th century and forced the mariners and merchants to settle at the current day Barbican near the river mouth. At the time this village was called Sutton, meaning south town in Old English. The name Plym Mouth, meaning "mouth of the River Plym" was first mentioned in a Pipe Roll of 1211. The name Plymouth first officially replaced Sutton in a charter of King Henry VI in 1440. See Plympton for the derivation of the name Plym.

Question:
In what century were sailors obligated to relocate from Plympton due to silting?

11th