What we know of the early Imperial liburna - structurally speaking - can be summed up in two words: not & much. It is commonly attested in funerary inscriptions, contracts, altars etcetera, as a type of ship. We know of a few dozen names of liburnae of the Misenate and Ravennate fleets and several names of ships in provincial fleets. It is a type of ship regularly mentioned in ancient literary sources as well. But what it looked like, can only be derived from those same sources. No remains liburnae have ever been found and then there are representative sources...These have their own problems of course, not to mention the fact that no image is ever positively identified as a liburna (oh, to have a grafito like the Alba Fucens one of a 'navis tetreris longa', ie: quadrireme).

So what can we say about the construction of the liburna? The best starting point is probably the number of rowers. Because once it is known how many men made up the rowing complement of the ship, you have an excellent indication of its lenght. The magic number is the interscalmium

Basically the interscalmium is the distance between two tholepins - the point where an oar swivels. It's optimal range is fixed by human physiology and it's know from an ancient source. According to Vitruvius , De Architectura I.2.4, the interscalmium was two cubits, or about 90 cm (~3 feet) long. Taking into account other fixtures, this length is confirmed in archaeological findings. So, once you know the number of rowers per side of the ship on a single row, you can make a pretty good estimate of the length of the mid-section of the ship (the prow and poop section are more difficult).

How many rowers sat on the benches of a liburna? Again, sources are few and far between and I'm going to ignore the possibility that river warships were smaller than their sea-going cousins. You could count the number of visible oars on reliefs that can be identified with some confidence as biremes, such as the Neumagen relief. The latter has 22 oars on one side, suggesting 44 rowers at least. The probable biremes on Trajan's Column would by this reckoning, have had only 22 rowers (in two rows!). The problem lies of course in the question of the reliability of these representations. We are dealing with the bireme depicted above where there is clearly no accurate relation between ship-size and crew members. So why should the number of oars be correct?

What about crew housing? Very few naval bases have been excavated, but the fort at Dover (UK) might supply us with the best indication for crew size. Barracks were excavated with eight rooms to a single block. Assuming they housed a contubernium of eight soldiers each like in other forts, and assuming one block represents a single crew, that would mean that the entire crew of a liburna - it is likely the Classis Britannica consisted mainly of liburnae as well - counted 64 rowers and sailors. I have argued elsewhere that the marines would be counted as a separate unit, so they would not be housed in the same block. One or two contubernia of sailors would be very likely, leaving 48-56 rowers. Interestingly, that would be almost the same number as the world's first bireme had, the Greek pentecontor, named after its crew of 50 men. Some more confirmation would be nice, hwever.

There is one archaeological element that might help confirm, or rather: constrain, the numbers mentioned above. Boathouses have been used very effectively in the reconstruction of the Athenian trireme. Housing the ship whenever it did not need to be in the water, to help preserve the wood, they indicate the outer limits of ship sizes. Sadly, very few Roman boathouses have been traced. None have been found either at Misenum or Ravenna - the main Roman naval bases - but in the provinces several were found in a fortified harbor on the Lippe river near the main legionary camp at Haltern (Germany), dating them to the very early Imperial era. They are about 28m long and some 6 meters wide. Undoubtedly the Romans left some space on either side and at the end, so maintenance could be performed and equipment could be stored, so the outer limit should probably be set to some 25 * 4 meters. Can that be calculated back to the number of crewmembers? To be honest, no, not for now, because we need to know how much of that 25 meters goes to the prow and poop. As long as that is complete guesswork, just one meter more or less will in- or decrease the number of rowers by four (2 rows * 2 sides)

Not very satisfying, I know, but then again, we just started researching this vessel. To be continued.