But from the time of Constantine's conversion, it is beyond doubt that the choirs were divided off from the other portion of the church by veils or screens. Eusebius describes the choir of the Church of the Apostles, erected by Constantine at Constantinople, as enclosed by screens, or trellis-work, marvellously wrought.—"Interiorem ædis partem undique in ambitum circumductam, _reticulato opere_ ex ære et auro affabre facto convestivit." The same writer thus speaks of the choir of the Church of Tyre, built and consecrated by the Bishop Paulinus:—"Porro sanctuario hoc modo absoluto et perfecto, thronisque quibusdam in altissimo loco ad Præsidum ecclesiæ honorem collocatis, et subselliis præterea undique ordine dispositis, decore eximieque exornato, altarique undique tanquam Sancto Sanctorum in medio sanctuarii sito, ista rursus, ut a plebe et multitudine eo non posset accedi, cancellis ex ligno fabricatis circumdedit, qui adeo artificiosa solertia ad summum elaborati sunt, ut mirabile spectaculum intuentibus exhibeant." The emperor Theodosius divides the church into three parts:—"Sacro sanctum Altare _Cancellis Clausum_, quadratum Templi oratorium murorum ambitu circumseptum, et locum residuum usque ad ecclesiæ fores exteriores." And St. Paulinus, Bishop of Nola, describes three doors in the screens of the Church of St. Felix. Trinaque Cancellis currentibus ostia pandunt. Among the decrees of the Second Council of Tours, in 557, it is ordered that lay persons are not to enter the chancel which is divided off by screens, except to receive the holy communion:—"Ut Laici secus altare, quo sancta mysteria celebrantur, inter Clericos, tam ad vigilias, quam ad Missas, stare penitus non præsumant; sed pars illa _quæ a Cancellis versus Altare dividitur_, Choris tantum psallentium pateat Clericorum. Ad orandum vero et communicandum laicis et feminis, sicut mos est, pateant Sancta Sanctorum." St. Germanus, patriarch of Constantinople, thus explains the intention and meaning of the choir screens:—"Cancelli locum orationis designant, quojusque extrinsecus populus accedit. Intrinsecus autem sunt Sancta Sanctorum solis Sacerdotibus pervia. Sunt autem revera ad piam memoriam _Cancelli ænei_,[5] nequis simpliciter et temere ingrediatur." The space enclosed by these screens in those churches where the aisles extended round the choir was entered by three double gates, those to the west, at the lower end of the choir, were called "the holy doors," the others were placed between the choir and the sanctuary, on the epistle and gospel sides. But in smaller churches, where the chancel alone forms the eastern extremity, there was only one pair of gates, or holy doors, at the west, and this most ancient arrangement has continued down to the present day, even in churches that have been fitted up with modern iron railings.