Real Life European Dual Sword Wielding

Not talking about that Musashi dude here, but I'm referring specifically about two swords. Yeah, it existed and people did it. Skeptical? Good, I like that. Here are the sources:

Ragione di adoprar sicuramente l'Arme, available in italian and english:
http://wiktenauer.com/wiki/Giacomo_di_Grassi#Double_Side_Swords
>There are also used now adays, aswell in the schools, as in the lists, two Swords* or Rapiers, admitted, and approved both of Princes, and of the professors of this art, for honorable and knightly weapons, albeit they be not used in the wars. Wherefore I shall not vary from my purpose, if I reason also of these, as far as is agreeable to true art. To him that would handle these weapons, it is necessary that he can aswell manage the left hand as the right, which thing shall be (if not necessary) yet most profitable in every other kind of weapon. But in these principally he is to resolve himself, that he can do no good, without that kind of nimbleness and dexterity. For seeing they are two weapons, and yet of one self same kind, they ought equally and indifferently to be handled, the one performing that which the other does, and every of them being apt aswell to strike as defend. And therefore a man ought to accustom his body, arms and hands aswell to strike as defend. And he which is not much practiced and exercised therein, ought not to make profession of this Art: for he shall find himself to be utterly deceived.

*Those are called "sideswords" nowadays, but that level of pedantic classification wasn't used in the times people actually fought with them.

https://www.youtube.com/watch?v=-1R-xZy-Gb4
>Dual-wielding with swords was done historically - context is the key
More videos about two-sword fighting:
https://www.youtube.com/watch?v=C2aCr5YfYKE
https://www.youtube.com/watch?v=jZNZyhNFSaE

Camillo Agrippa's combat treatise scan:
https://archive.org/details/bub_gb_p8OnsLhUQBMC

Opera Nova, available in italian and english
http://wiktenauer.com/wiki/Achille_Marozzo

http://www.umass.edu/renaissance/lord/collection.html
Collection of scanned treatises and manuals about swordsmanship.

http://www.schoolofthesword.com/Twos%20Company%20PartIII.pdf
http://www.schoolofthesword.com/Twos%20Company%20PartIV.pdf
Practical aplications of sword+buckler and sword+sword according to Marozzo's treatise, by Phil Marshall and Oliver Barker.

TL;DR: It was done historically. It had the following disadvantages:

-You need at the very least three times more training than with a single sword, because you have to learn to use it with your right hand, then learn with your left, to finally learn to use both without one disturbing the movements of the other.

-Di Grassi warns that this style should be used only at tourneys and duels, never wars. That's because dual handling demands too much concentration for one to focus on the kind of cooperative coordination that makes the difference between a bunch of warriors and an army.

-Last but not least, it should be used against enemies with few to no armor. The reason is that a single sword used with both hands brings you the necessary power and precision to find weak points and target joints, be it a plate harness or a gambeson.

The adavantages were:

-Everything the right hand does, the left does as well, as both have equal reach. The "secondary" weapon is up for you to decide, and it may be the other one second later. The average swordsman already has some trouble fighting left-handed warriors, but he's going to have a hard time trying to guess which hand is feinting and which hand is actually attacking, for you can do both at the same time with either!

-Because dual wield is so hard to accomplish, users of this style are sure to enjoy fame at tourneys, impressing the public and competitors alike.