As well as their disciplined formation and formidable tactics, Imperial Roman armies used their advanced technology to produce a variety of artillery pieces, of which the arrow-throwing ballista or scorpion was a common example. Although apparently not often used in battle, they were principally weapons used in the assault on or defence of fortifications. However smaller examples were taken with armies and used in the field, and the model in this set is about as small as they are likely to get, so not a siege item.
LW have already made one of these machines (Set 42), but this one is very much smaller - less than half the size. It is also much inferior in terms of build quality and detail. The soft plastic does not help, but we found that some pegs were too large, and the model is quite wobbly. The support for the arrow bed interferes with the main leg of the device, unless the leg is meant to be the other way round - since there are no instructions or even a picture we can only guess at the assembly! The front of the ballista, where the coiled rope springs are, has not been detailed at all on one side, so the whole thing is really basic. In our example we placed the spring housing on top of the arrow groove, but to allow the arrow to leave the device this must be in front of the groove, although this would be an extremely weak glued join and still a long way from accurate.
The figures have all been seen before in other LW sets, and as a result are an odd mixture of styles and time periods. A couple have had a shield added to make it seem like a new pose, but no one is going to be fooled. All but one have nothing to do with the ballista and are presumably just there to bulk out the set a little. The second figure in the top row is the exception, as he seems to be carrying a supply of bolts for the machine, but there is no one here actually interacting with it, so you could hardly say the weapon came with a crew. As usual, the figures are fairly flat and quite ugly.
HaT have had a similar product (Roman Catapults) out for several years and this is still in production, so why would LW make much the same thing, even if they label it as imperial rather than republican? The HaT model is by far the superior of the two, and you get a lot more with it too, so we can think of no good reason why anyone would want to purchase this offering. Well worth avoiding.