Sorry not to have noticed this until now. :oops:
This is a difficult question to answer accurately. Many of the known examples come from unstratified watery contexts, making precise dating difficult and this task is not aided by the fact that the contexts of many other examples were not recorded in the sort of detail which we would like to see today. Added to that, the standard of publication is also highly variable, with some examples, such as the Velsen and Titelberg daggers being given excellent treatment, whilst some others have been derisively poor in their level of reporting.
That said however, there are certainly a few things which can be said.
All three first century AD sheath types (Type 'A', Type 'B' and Frame type) are probably derived from Iberian predecessors, with the type 'B' possibly being derived from a Spanish type which incorporated something similar to a Roman type 'B' front plate within a frame.
We know that type 'B' sheaths were in use by the late AD20s, as the Velsen soldier was buried in around AD28 (at the time of the demolition of the fort), so we know that all three types were in use side by side for some time at least. We also know that type 'A' sheaths were in use at least as late as the early AD80s, as the sheath fragment from Corbridge is of type 'A'.
Decoration can also be a useful tool for us. The vast majority of sheaths which have been found were hight decorated (in fact I know of only four which were not) and there are a number of different decorative styles (Scott defines ten styles and also a small miscellaneous group, whereas Obmann defines four much more general style categories). Some at least of these decorative styles were subsequent to each other, suggesting that like belt plate styles, dagger sheaths may have been subject to ideas of fashion. This is nowhere better illustrated than by a type 'B' plate from Xanten, which was decorated on both sides, showing that a plate featuring an earlier style of decoration was removed, turned over, and redecorated in a later, more fashionable, style.
You might be interested in this, quoted from the Summary page of Obmann:
"On Group 1 sheaths, copper alloy and enamel inlays were used exclusively, frequently to produce garland and rosette motifs. The same materials were used for Group 2, but flat silver wire inlay and new decorative elements such as peltae and double-axes were introduced. Group 3 sheaths have no enamel inlays, copper alloy is found infrequently and silver predominates. The new motifs are palm fronds and rhomboids. The motifs on Group 4 sheath plates are more abstract and the technical execution is often extremely poor."
(Jurgen Obmann: Studien zu roemischen Dochscheiden des 1. Jahrhunderts n.Chr. 2000)
I would add to this that all of these, but particularly examples in groups 1 and 2 may feature addition patterns of decorative rivets.
It is interesting to note that virtually none of the type'B' sheath plates so far known incorporate copper alloy in their decoration. Obmann's group 1 is dominted by type 'A' sheaths. Similarly, Obmann's group 4 is dominated by type 'B' sheaths.
It is also probably worth mentioning here that the grip plates of the daggers themselves were often decorated to match the decoration on the sheath. The best known example of this is the Leeuwen example, where the iron grip plate has be covered with a thin layer of copper alloy and decorated with pearled strip to match the decoration of its copper alloy sheath.
To refer now to the example you gave, unfortunately for you, both the Leeuwen and the Melun sheath are unique examples which do not conform to standard decorative patterns. Other examples in this miscellaneous category include the Usk 1 sheath, an example from Xanten and a pair from Dangstetten which are decorated exclusively with zig-zag patterns of rivets.
The type usually ignored, but nonetheless also present alongside the other two types, is the frame type sheath. Far few of these are known and the number is limited to either six or seven (depending on whether or not two of the fragments from Dangstetten originally belonged to the same sheath) examples. The Titelberg dagger comes from a context early in the first century AD but already the pommel expansion on the handle has the shape of other first century AD pommel expansions (like a circle with the top sliced off, often decorated with large headed nails driven into the flat top surface). The sheath from Exeter, which must have been deposited in the fifteen years or so after the invasion of Britain, has the same general dimensions as the Titelberg sheath but he construction method is different. We can possibly, in that case see a line of development in the iron frame sheath, moving from the examples for Dangstetten, to the Titelberg example and on to the Exeter example. Frame type sheaths were certainly in use into the second century AD but what form they had developed by then is open to speculation. Unfortunately their construction tends to be fairly lightweight and it is reasonable to suppose that the majority have simply rusted away to leave no recognisable trace.
It is also not possible to know how (if at all) frame type sheaths were decorated. The Titelberg sheath preserved a very fine inscribed decoration on one of its cross hangers but not on the other. It is not possible to determine whether similar decoration was to be found on the other examples, all of which are more rusted. It is possible that the leather visible between the frame elements would have been decorated but if so we can do little more than guess as to what form this might have taken.
The daggers associated with frame type sheaths appear to have been of the normal types, and it is reasonable to think that like the Titelberg example their grips were of standard types as well, although it should be noted here that the Tarent example seems to have featured a cruciform pommel expansion.
Finally, a mention of tangs. Although most people today seem to assume that the tangs of daggers were of the same shape as the grip plates, this was not necessarily the case. Tangs of this sort are known as 'frame' (or type 'I') tangs and appear to become less common as the first century AD progresses. Some of these frame tangs (such as that on the Titelberg dagger and on another example from Colchester) end short of the pommel expansion. As the first century AD progressed it appears that narrow 'rod' (or type 'II') tangs became more common and came to dominate, probably leading to changes in the internal structure of handles, although grip plates do not appear to have changed, as can be seen from the example of Usk 1, which features a rod tang between to iron grip plates of normal type.
I hope this goes some way to answering your question.
Crispvs
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