ASTRAGAL, (from acpaya),og, the heel-bone,) a mould ing of a semicircular section, projecting from a vertical dia meter. It is remarkable that Vitruvius does not mention any astragal between the shaft and the hvpotrachelion of the Doric and Tuscan columns, as is to be found in the Doric of the theatre of Marcellus, at Rome-; so that it is probable, the hypotrachelion might be formed without any mouldings what ever, by making it recede in a small degree within the shaft, or by fluting it, as in the column of Trajan. This doctrine is also very conformable to all the Grecian examples of the Dorie order ; for the hypotrachelion is separated from the shaft by one, two, or three annular channels, without any projecting moulding, and the flutes are continued upwards through the hypotrachelion, to meet the under side of the annulets. In the Ionio order of the temple of Ereehtheus, at Athens, the hypotrachelion is however separated from the shaft by an astragal ; and in the temple of Minerva Polias, at the same place, they are separated by a plain fillet.
In all the other numerous Grecian examples of this order there is no hypotrachelion : the astragal is placed imme diately below the echinus. The same is to be found in the few remaining Roman examples of this order. In the Corin thian and Composite orders, the astragal is never omitted between the under row of leaves and the shaft. except in the Corinthian of the monument of Lysicrates, at Athens, which is one of the oldest examples of this order ; where, instead of the astragal, there is an annular groove, from which, and from the beauty and delicacy of this example, it seems pro bable that the astragal might be originally formed of a metal ring.
The astragal is a moulding of very frequent application, not only at the upper ends of the shafts of columns., but also in their bases and entablatures. It is the simplest of all monI anll the only one winch can stand alone by itself, and project from a plane surfiice without the aid of a fillet or straight part.
The Greeks and Romans frequently cut their astragals into beads, formed alternately of oblate and prolate sphe roids, or, instead of prolate spheroids. figures consisting of double cones, with cylindrical parts between, are intro duced : this practice is tulluwed by the moderns with various innovations.
In the Egyptian architecture, we meet frequently with clusters of astragals, circninseribing the shafts of the columns ; in various places dividing them into several compartments, of which sonic of them are frequently receded vertically with astragals. The capitals often join upon the tops of the shafts, without any horizontal moulding between them.
The astragal mid torus are exactly similar figures: the only distinction is, that when they are compared with the other, hi the same piece of work, the torus is large, and the astragal small, perhaps not exceeding one-third part of the diameter of the torus; hut in most eases any propor tion less, so that it may be sufficiently distinct.