[Illustration: SCULPTURE FROM SANT' ABBONDIO, COMO, 5TH CENTURY. (THE CIRCLE AND CENTRE A SINGLE STRAND.) _See page 84._] There is a marvellous knot sculptured on a marble panel of the ninth century from S. Ambrogio Milan, which Cattaneo has illustrated.[67] The whole square is filled with complicated interweavings of a single strand, forming intricate loops and circles, the spaces between which are filled with the Christian emblems, the rose, the lily, and the heart. Another _pluteus_, originally from San Marco dei Precipazi at Venice, but now over the altar at S. Giacomo, is dated 829 A.D., and is covered with what seems at first sight a geometric pattern of circles and diamonds, but if analyzed will be found a single strand interwoven in the most mysterious and beautiful manner. It seems that the parapet of the tribune in all these early Basilicas was the place chosen especially by the Roman architect of the third and fourth centuries, and the Comacine of the eighth and ninth, to set their secret and mysterious signs upon, and to mark their belief in God as showing infinity in unity. It is very curious to notice in the churches which the guild restored in the thirteenth and fourteenth centuries, when their tenets had altered, and their sign changed, how they themselves removed these old stones, but yet being careful not to destroy them, they turned them and sculptured them again on the other side. In the excavations or restorations in Rome many of the _intrecci_ have come to light at the back of panels of Comatesque pulpits, recarved into altar frontals, or used as paving-stones before the altar. Some of the earlier and less intricate forms of knots may be seen in the church of S. Abbondio at Como, which was built in the fifth century and again rebuilt in the ninth. Some excavations in the last century revealed the foundations of the fifth-century church, and also brought to light a number of sculptured stones which had been turned face downwards to form the pavement. We give illustrations from two of these which have the Comacine signs plainly written on them, and show even in this early and simple form the reverence for the line of unity. Cattaneo thinks they may have formed the front of the gallery above the nave in the eighth-century building.