Derived from the French for "wing," an aisle, historically, was an extension of a side or "wing" of the nave. It was built to enlarge the seating capacity of the church. This extension typically had a separate and lower roof. The aisle was separated from the central nave of the church by a passageway. The term was eventually applied to the passageways themselves, including the central passageway of the nave or "center aisle." Although the expression "center aisle" is technically a contradiction of terms, it is common usage in the church today.