In looking at some of the swords Albion makes and reading the historical descriptions, I got to wondering how often weapons from different cultures may have crossed over to the other side by being picked up on the battlefield.
For example, how would you really know whether a Viking or a Saxon had brought a particular sword to the battle? Given that the technology of both sides of that conflict was already pretty similar, it doesn't seem logical that a swordless Saxon who managed to "liberate" a sword from its previous owner would have had any problem adopting it as his own. It would also seem that as groups had increased contact with each other, styles and technological advances would also probably cross back and forth between cultures.
In cases like this, how would we know who brought what to the fight?
Just wondering how historians go about figuring these things out.

Historians probably try to figure out where the weapons were made, rather then who carried them in a battle because of the reasons you mention.

The problem with only finding out where the sword was made is; maybe it wasn't typical for that place.

Example: Medieval Serbia imported weapons from Ragusa. BUT documents mention they made a specific type for the Serbs, not the same they used themselves. I think the same was true of armour (I'm not sure), they made serbian style armour when exporting there. So if one found out that it was all made in Ragusa, it would paint a wrong picture of what stuff was in use in Ragusa.

Battlefield pick-ups are not just about ancient or medieval history as soldiers always seen to think that the other guy's equipment is better than theirs and in some cases they are right.

In WWII a lot of soldiers would pick-up and use an MP40 or an MG42 and even enemy tanks were used by both sides when captures in working condition: Really obvious markings added to them to avoid friendly fire though was needed. ;) :lol:

Using an enemy gun also has a sound signature that could fool the enemy being fired at and make finding from where the shots were coming from more difficult: So there are advantages to using the other guy's stuff as well as using their ammunition supply when deep into their rear.

It's still going on-a while back I saw an Iraq press shot of two of our guys in full battle rattle carrying AKs.

In the case of vikings and saxons, the estimations are based on what they brought witht them in their graves, not what they fought with. One also has a rather large selection of dark age weapons, due to the fact that they burried them in well marked places (graves)
While there might have been some exchange of weapons, the different regions still have their overall styles. Over time these could influence each other as well.

During my two tours, US forces were not authorized to use anything other than US issued weapons. In fact, to possess a functioning enemy weapon on a FOB/PB is against SoP. I know that in a combat scenario (ie, you were clearing a house and you ran out of ammo) or you are imbedded with an SF team (in which case you will probably carry what the enemy is carrying so you don't have to rely on ammo resupply) - you can use whatever you find that shoots. I'd question a photo taken of a US soldier using an enemy weapon in an actual firefight - unless it was one of the two above examples.

Now, there were plenty of AKs, RPKs, SKS, and Dragonovs around that the IPs and IAs use for training; and you can shoot these at the range if you so desire. I've got a picture of myself on a camel wearing a tribal shemagh and brandishing a Krink - but I never did a convoy or MOUT like that.

I do have an AK bayonet bring-back though. It's about all that customs will let you get back OCONUS with.

Back on topic, I would think that in antiquity that this was a quite common practice. I imagine that early on, weapons and armor were merely picked up and reused. Later on, items may have been recycled (smelted down and reforged) - especially if the salvagers were further along in their knowledge of metallurgy. However, this is just speculation on my part without a historical reference.