The mortar battery was popular with tourists as it offered a safe view on the besieged city because it was behind the allied trenches and out of range of Russian artillery. The photograph is one from a series by the royal photographer Roger Fenton (1819–1869), which he made to create a topographical overview of the theatre of war.
Roger Fenton (1819–1869), A Quiet Day at the Mortar Battery, collodion photograph, 1855; source: Library of Congress LC-USZ62-2320, http://www.loc.gov/pictures/item/2001697674/.