As soon as Christianity had triumphed in the Roman Empire, thus becoming the religion of the rich and powerful as well as the religion of the poor and lowly, more attention was devoted to the conduct of worship. Magnificent church buildings were often erected. Their architects seem to have followed as models the basilicas, or public halls, which formed so familiar a sight in Roman cities. [6] Church interiors were adorned with paintings, mosaic pictures, images of saints and martyrs, and the figure of the cross. Lighted candles on the altars and the burning of fragrant incense lent an additional impressiveness to worship. Beautiful prayers and hymns were composed. Some of the early Christian hymns, such as the _Gloria in Excelsis_ and the _Te Deum Laudamus_, are still sung in our churches. Organs did not come into use until the seventh century, and then only in the West, but church bells, summoning the worshiper to divine service, early became attached to Christian edifices. [Illustration: RELIGIOUS MUSIC From a window of the cathedral of Bourges, a city in central France. Shows a pipe organ and chimes.] SUNDAY The Christians from the start appear to have observed "the first day of the week" [7] in memory of Christ's resurrection. They attended public worship on the Lord's Day, but otherwise did not rigidly abstain from worldly business and amusements. The Jewish element in some churches, and especially in the East, was strong enough to secure an additional observance of Saturday as a weekly festival. Saturday long continued to be marked by religious assemblies and feasting, though not by any compulsory cessation of the ordinary occupations. During the fourth century Sunday, as the Lord's Day was now generally called, came more and more to be kept as a day of obligatory rest. Constantine's Sunday law [8] formed the first of a long series of imperial edicts imposing the observance of that day as a legal duty. In this manner Sunday, like the Jewish Sabbath on the seventh day of the week, was dedicated wholly to the exercises of religion. FESTIVALS The great yearly festivals of the Church gradually took shape during the early Christian centuries. The most important anniversary to be observed was Easter, in memory of the resurrection of Christ. A period of fasting (Lent), which finally lasted forty days, preceded the festival. Whitsunday, or Pentecost, was celebrated on the fiftieth day after Easter. [9] Two other festivals of later adoption were Christmas, the celebration of which was finally assigned to the 25th of December, [10] and Epiphany (January 6), commemorating the baptism of Christ. In course of time many other feasts and fasts, together with numerous saints' days, were added to the calendar of the "Christian Year." 121. EASTERN CHRISTIANITY EXPANSION OF CHRISTIANITY IN THE EAST