Early Christian art developed from the 1st to 5th centuries AD. Key events that influenced its development included the spread of Christianity by St. Paul and its acceptance by Emperor Constantine in the 4th century. Art forms included frescoes, mosaics using small cubes called tesserae, sculptures, and illuminated manuscripts with illustrations and ornamental borders. Mosaics became more advanced and were used to decorate walls and vaults of churches. Illuminated manuscripts were decorated gospel books that were costly to produce. Ivory carvings were made into luxury religious objects like boxes and diptychs. The era saw the rise of early Christian basilica churches that set the architectural template for future churches.