Task: Question Answering
Input (English): Passage: In the following century Ravenna, the capital of the Western Roman Empire, became the center of late Roman mosaic art (see details in Ravenna section). Milan also served as the capital of the western empire in the 4th century. In the St Aquilinus Chapel of the Basilica of San Lorenzo, mosaics executed in the late 4th and early 5th centuries depict Christ with the Apostles and the Abduction of Elijah; these mosaics are outstanding for their bright colors, naturalism and adherence to the classical canons of order and proportion. The surviving apse mosaic of the Basilica of Sant'Ambrogio, which shows Christ enthroned between Saint Gervasius and Saint Protasius and angels before a golden background date back to the 5th and to the 8th century, although it was restored many times later. The baptistery of the basilica, which was demolished in the 15th century, had a vault covered with gold-leaf tesserae, large quantities of which were found when the site was excavated. In the small shrine of San Vittore in ciel d'oro, now a chapel of Sant'Ambrogio, every surface is covered with mosaics from the second half of the 5th century. Saint Victor is depicted in the center of the golden dome, while figures of saints are shown on the walls before a blue background. The low spandrels give space for the symbols of the four Evangelists. Question: When was the baptistry at the Basilica of Sant'Ambrogio demolished?
Output (English): the 15th century