Fig. 3.—Type II. with turned-up and elongated catch-plate. a, "Leech" fibula; b, "Boat" fibula; c. variation of "Boat" fibula.
The example shown in fig. 7 is an ornate development of type II. above.
In the later Iron Age (or early La Tène period) the prolongation of the catch-plate described in the second and fourth groups above has a terminal knob ornament, which is reflexed upwards, at first slightly (fig. 8), and then to a marked extent, turning back towards the bow.
A far-reaching change in the design was at the same time brought about by a simple improvement in principle, apparently introduced within the area of the La Tène culture. Instead of a unilateral spring—that is, of one coiled on one side only of the bow as commonly in the modern safety-pin—the brooch became bilateral. The spring was coiled on one side of the axis of the bow, and thence the wire was taken to the other side of the axis, and again coiled in a corresponding manner before starting in a straight line to form the pin. Once invented, the bilateral spring became almost universal, and its introduction serves to divide the whole mass of ancient fibulae into an older and a younger group.
Fig. 4.—Type III with disk for catch-plate, and convoluted bow.
With the progress of the La Tène period (300-1 B.C.) the reflection of the catch-plate terminal became yet more marked, until it became practically merged in the bow (fig. 9). Meanwhile, the bilateral spring described above was developing into two marked projections on each side of the axis. In order to give the double spring strength and protection it was given a metal core, and a containing tube. When the core had been provided the pin was no longer necessarily a continuation of the bow, and it became in fact a separate member, as in a modern brooch of a non-safety-pin type, and was no longer actuated by its own spring.
The T-shaped or "cross-bow" fibula was thus developed. During the first centuries of the Empire it attained great size and importance (figs. 10-12). The form is conveniently dated at its highest development by its occurrence on the ivory diptych of Stilicho at Monza (c. A.D. 400).
In the tombs of the Frankish and kindred Teutonic tribes between the 5th and 9th centuries the crossbar of the T becomes a yet more elaborately decorated semicircle, often surrounded by radial knobs and a chased surface. The base of the shaft is flattened out, and is no less ornate (fig. 13). At the beginning of this period the fibula of King Childeric (A.D. 481) has a singularly complicated pin-fastening.