We have now to consider the external influences which came into play after the introduction of Christianity (_circa_ A.D. 450). First amongst these was the influence of Italy, and thus more indirectly that of Byzantium. It is to this source that it is possible to trace the interlaced-work and scrolls of foliage which occur so frequently on the early sculptured monuments in Great Britain. We can refer to no better text-book whilst dealing with this portion of our investigation than _L’Architettura in Italia_, by Professor Raffaele Cattaneo (Venezia, 1888), who, by a careful study of the subject, has been able to divide early Italian ecclesiastical architecture into the following styles and corresponding periods:— (1) Latino-Barbaro A.D. 300 to A.D. 600. (2) Bizantino-Barbaro A.D. 600 to A.D. 800. (3) Italo-Bizantino A.D. 800 to A.D. 1000. As an example of the first period we have the Ciborium in the Church of San Clemente at Rome (A.D. 514-23), decorated with plaitwork and foliage, both evidently of Classical origin. Belonging to the second period we have the Ciborium of San Giorgio di Valpolicella[443] (A.D. 712), decorated with broken plaitwork, and the Baptistery of Cividale (A.D. 737), with fully developed knotwork. And belonging to the third period the Ciborium of Sant’ Apollinare in Classe, near Ravenna (A.D. 806-16), with interlaced-work and foliage, and a slab over the altar of San Giacomo, at Venice (A.D. 829), with circular knotwork.[444] [443] Also the jambs of the doorway of the chapel of S. Zeno in the church of S. Prassede, Rome (A.D. 772-95). [444] Slabs of circular knotwork are also to be seen in the church of Sta. Sabina, Rome. [Illustration: CIRCULAR KNOTWORK ON SLAB IN CHURCH OF STA. SABINA, ROME] [Illustration: CIRCULAR KNOTWORK ON SLAB IN CHURCH OF STA. SABINA, ROME] [Illustration: DOORWAY OF THE CHAPEL OF S. ZENO IN THE CHURCH OF S. PRASSEDE AT ROME, SHOWING BROKEN PLAITWORK ON JAMBS (A. D. 442 TO 795)] [Illustration: Pierced Marble Screen at Ravenna] A careful examination of these specimens shows that the plait was the first kind of interlaced-work employed for decorative purposes, and that it was of Classical origin. The plait as a decorative motive must have been well known to the inhabitants of this country during the Roman occupation and immediately after, from the numerous examples which occur on Roman pavements, as at Lydney Park, Gloucestershire, and elsewhere.