Paris's oldest church was first built to shelter a relic of the true cross brought back from Spain in AD 542. The Romanesque square tower dates from the early 11th century, while the chancel was enlarged and the church then reconsecrated by Pope Alexander III in 1163, after no less than four sackings by the Vikings. The colorful 19th-century frescoes in the nave are by Hippolyte Flandrin, a pupil of the classical master Ingres. The church stages superb organ concerts and recitals. Weekdays 8-7:30, weekends 8 AM-9 PM. Métro: St-Germain-des-Prés.