To the jambs we may apply the same process, either substituting a colonnette for the inner order, and pilasters for the outer ones, or _vice versa_ (Figs. 292, 293), or substituting colonnettes or pilasters for all. I do not know how early this system of using colonnettes to do merely decorative duty was introduced. We have a specimen of it in the remains of the church built by Benedict Biscop, at Monk Wearmouth, in the seventh century, where, as I have stated in a previous lecture, two baluster shafts are placed in either jamb of a doorway to support the impost.[34] To go to the far East, we find the system in use in the Mosque of Touloun, at Cairo, built, I believe, in the ninth century. In one of the doorways of the cathedral at Mayence, built about the end of the tenth century, columns and pilasters, with Corinthian capitals, and crowned by a thick impost moulding, are alternately employed to carry the four receding orders of the arch. The whole has semi-Classic details. In the western portals of St. Mark’s, at Venice (close upon the same period), we find a profusion of detached columns similarly used. They are of marble and other rich materials, and were probably brought to Venice from ancient buildings in the East. [Illustration: Fig. 290. Fig. 291. Fig. 292. Fig. 293.] It may be that the possession of such antique relics, and the long-established practice of re-using them, may have suggested the use of small columns for such purposes; indeed, it is curious that in the case of the Mosque of Touloun, just alluded to, as a very early instance of the use of colonnettes, there is a tradition that the architect, who was a Christian, was imprisoned for refusing to use the columns torn [Illustration: Fig. 294.--Cloisters of St. Paul without the Walls, Rome.] from desecrated churches, which had been a condition prescribed to him, and only consented to proceed with the work on the withdrawal of this order. Whether or not, this custom originated the feature under consideration, I think that it is one which belongs essentially to a _derivative_ style, and would hardly have come into existence in a style of architecture not aided by traditions of the past. The Romans themselves, as is proved by their mural paintings, seem to have indulged in the use of thin columns (possibly of metal), for buildings not demanding massive dignity; and it is just possible that in their domestic architecture some suggestions of this use of such pillars might have existed; and certainly among Mediæval works, in none are they more charmingly introduced than in the cloisters of St. Paul without the Walls, and St. John Lateran, at Rome, whose details are much more Classic than Gothic (Fig. 294). In our Norman buildings colonnettes are for the most part built in the solid of the piers, which would suggest that they are not there in the earliest stage of their use.