LONDON — Greenpeace activists scaled the columns in front of the British Museum on Thursday morning, attaching and then unfurling banners that protested the oil company BP’s sponsorship of a new exhibition, “Sunken Cities, Egypt’s Lost Worlds.” The museum was closed until 2 p.m., “to ensure the safety of the museum’s visitors,” a spokeswoman said in an email. Eleven people were arrested in connection with trespassing.

There have been protests against other BP-sponsored exhibitions at the museum, including “Shakespeare: Staging the World” in 2012, and “Vikings: Life and Legend” in 2014, but this was the first time the museum had to close.

The protest follows another made by the theatrical group “BP or not BP” on Tuesday evening during a V.I.P. reception for “Sunken Cities,” which displays artifacts from two lost Egyptian cities buried under the sea.