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human
[Star Wars] Has there ever been a large scale battle of Jedi vs Sith?

I'm talking hundreds of lightsaber users just going at each other. In legends or canon. Not even Jedi and Sith specifically, just lightsaber users.
gpt
In the Expanded Universe/Legends there are several battles that fit your criteria.

The Great Sith War of 2996 BBY had many such battles, and was one of the earliest wars to have battles like that.

The Jedi Civil War (the conflict that Knights of the Old Republic takes place during) also had many battles between large numbers of Jedi and Sith.

The Great Galactic War (the war that the Old Republic MMO takes place during) had plenty of battles in which many Jedi and Sith took part.

The last of the great wars to include massive numbers of Jedi and Sith taking the field was the New Sith Wars that lasted from 2000 BBY until 1000 BBY. The most climactic of this war's battles was its last battle, the Battle of Ruusan. The Battle of Ruusan was fought between the armies of the last great Sith empire, the Brotherhood of Darkness, and the Army of Light, which was a joint effort between the Jedi and the Republic. 
This war was so devistating, that many systems had to be taken under the direct control of the Jedi, and a Jedi was almost always elected Chancellor of the Republic. The systems controlled by the Jedi became little fiefdoms of certain Jedi Masters, who were referred to as the Jedi Lords, ruling over the their kingdoms as enlightened despots.

By the time of the battle of Ruusan, the Sith had lost all the territory they gained due to the fact they had been greatly weakened by infighting as the Republic and Jedi continued to gain strength. 

The most influential and powerful Jedi Lords, Lord Hoth, assembled his army, the Armies of his fellow Jedi Lords, the Jedi Order, and the Republic military calling this coalition the Army of Light. Lord Hoth led the campaign to destroy the Sith once and for all. Eventually the last great Sith army, the Brotherhood of Darkness, gathered on Ruusan to make their final stand.

The battle was long and bloody. Both sides sustained massive amounts of casualties, but the Sith's resources were far more limited than their adversaries in the Army of Light. So, as the battle dragged on, the Sith Started losing more and more ground to their foes. Eventually, in their desperation, the Sith unleashed their ultimate weapon, the Thought Bomb. The Thought Bomb was a special Sith force technique used by many Sith simultaneously, it created an explosion that engulfed all living things for miles around. The Thought Bomb killed many of the Army of Light's troops and all of the Brotherhood of Darkness, save for one Sith Lord, Darth Bane, who would go onto establish the Rule of Two and preserve the Sith in secret.

A monument was erected to honor the fallen from the Army of Light, called the Valley of the Jedi at the site where the Thought Bomb went off. Unknown to those who erected the monument the souls of all those who died from the Thought Bomb would be trapped in the Valley of the Jedi, creating a force nexus that could increase someone's raw force power if they were to enter it. Unfortunately the location of the planet Ruusan and the Valley of the Jedi were lost, due to changing star charts and some topographical errors. The plAnet's location would eventually be discovered by Jedi Master Rohm, who gave this information to Reblel sympathizer, Morgan Katarn, before he was slain by the Dark Jedi Jerec, and Morgan gave the Valley's location to his son, Kyle via a secret holo-recording tgt he hid away to give to him at a later time  (he died before he could give it to him directly so Kyle had to find it himself). The trapped souls were freed many centuries later when Rebel commando-turned Jedi Kyle Katarn, son of Morgan Katarn, defeated Jerec in the Valley, fulfilling a prophecy that stated that a hero would free the trapped souls after defeating a great evil in the Valley.

Large scale, Jedi vs. Sith battles would not be seen again until the Sith-Imperial war over 130 years after the Battle of Yavin, as the New Jedi Order and the Imperial Knights fought Darth Krayt's One Sith.