During the Roman occupation of England, missionaries came to her from Rome, the metropolis, and made converts, as they did in other countries, and as missionaries do nowadays in China and elsewhere. They and travelling merchants insensibly introduced the style of architecture then prevalent in Italy, namely, the Romanesque. Owing to the untutored nature of the Anglo-Saxons, their first attempts at imitating what would appear to them entirely new, together with the difficulty of procuring skilled labour, were necessarily crude. These first attempts may justly come under the heading of "Anglo-Saxon." When the Campanile or tall bell-towers came into existence in Italy, England imitated. _Anglo-Norman._--1066.--The Normans, at the Conquest, introduced their rendering of architecture, which they had borrowed from the Romanesque, with a suspicion of Lombardic, and even Byzantine styles intermingled. As they could not entirely at first uproot the local peculiarities of the Anglo-Saxon treatment of style which they found in the country, they in a way grafted the Norman architecture on to the existing style. Thus it came to be called "Anglo-Norman." At first the work was heavier in character than the Norman proper, but it became lighter towards the close of the twelfth century. _Norman Peculiarities._--The Norman peculiarities were the building of the church on a cruciform plan, with a square tower placed over the transepts where they cross the nave; the massive cylindrical nave piers. To relieve the heaviness of these massive nave piers and doorways, the chevron, or zigzag pattern, spiral and other groovings were cut. The mouldings were of the same character as in France, but towards the close of the twelfth century they were by degrees disused. In the transition period, 1154-1189, the dog-tooth ornament appears, and occurs in combination with the "billet," a circular roll with spaces cut away at intervals, as at Canterbury. The Normans also greatly employed arcades, both blank and open. The interlacing of arcades was frequently used by them. They were formed by semi-circular arches, intersecting each other regularly. This interlacing is supposed by many authorities to have been the origin of the "pointed lancet arch." The Norman arcades form a prominent feature in the internal and external decoration of their buildings. The internal arrangement of the larger churches consisted of three stages or tiers. The ground stage carried semi-circular arches, above that came the triforium, or second stage of two smaller arches supported by a column, and within a larger arch. Above this again, came the third stage or clerestory, with two or more semi-circular arches, one of which was pierced to admit the light. The nave was usually covered by a flat ceiling, and not vaulted. The crypts and aisles were vaulted.