Dominated by the dome of the Mother Church Extension, the Christian Science complex is the largest open public space in the Back Bay. The original Romanesque Revival church and bell tower initially rose on a constricted triangular lot, providing seating for a congregation of one thousand and a special retiring room for Mary Baker Eddy, founder of the Christian Science movement. An amalgam of Byzantine and classical architecture, the adjacent Church Extension was built to accommodate the rapid growth of this denomination. The basilica is renowned for its large pipe organ in an auditorium that seats three thousand. The semicircular classical portico with well-crafted Corinthian capitals was built as the main entrance in 1973.