The Battle of Kursk was one of the largest deployments of men and material ever assembled in the history of warfare - it was certainly the largest deployment of armor ever seen, although it depends on how you compare numbers and casualties to other battles like Stalingrad - which was certainly deadlier, but lasted 6 months and was a veritable meat grinder for both sides that were engaged in the besieged fortress
the Red Army deployed
1,910,361 men
5,128 tanks
25,013 guns and mortars
2,792 to 3,549 aircraft
against the Wehrmacht's
912,460 men
2,928 tanks
9,966 guns and mortars
2,110 aircraft
soviet losses were
254,470 killed, missing or captured
608,833 wounded or sick
6,064 tanks and assault guns destroyed or damaged
1,626 – 1,961 aircraft
5,244 guns
with the Wehrmacht losing
89,833 killed or missing
215,732 wounded
Estimate 760 tanks and assault guns destroyed,
681 aircraft (for 5–31 July)
The battles around Prokhorovka and the outlying villages around Kursk were some of the fiercest and most contested points in the entire war. Entire Soviet tank armies would face off against elite divisions of the SS tank corps such as 1st SS Liebstandarte, 2nd Das Reich, 3rd Totenkopf, and 5th Wiking divisions. The battles were fanatical, bloody, confusing, and disorienting. Tanks would fire point blank at each other obfuscated by smoke and fires of the raging battle. The Wehrmacht in Operation Citadel had to assault a well fortified and prepared soviet defense around the salient of Kursk created after the disaster at Stalingrad and their ensuing counter offensives. The Soviet's knew it was the Wehrmacht's first choice of attack, but had also been fed the exact start date of the offensive and its plans by the Lucy Spy Ring.
The result caused the evaporation of all German offensive capabilities on the Eastern Front and forced them into a permanent defensive mindset to hold all ground they had - preventing anymore soviet incursions towards the German Fatherland.
Source: Numbers came from Wiki for expediency
Well the Battle of Changping in China (260 BC) between the states of Qin and Zhao had roughly 1.1 million soldiers deployed and 700,000 casualties as the state of Qin was victorious leading to the Qin unification of China.
N.B. the numbers are all estimates and not 100% reliable as we do not have any primary sources detailing them. Also the number of casualties is including those who were buried alive once they had been captured.
If you are interested as to how the battle panned out there is a small story attached: For a few year the main Qin and Zhao armies had been playing a game of cat and mouse never really engaging and so never sustaining any major losses. This was due to the Zhao leader, Lian Po believing that waiting the enemy out was the best plan of action. However over time rumors spread that Lian Po was acting out of cowardice and so he was replaced with Zhao Kuo, son of a famous general, Zhao She.
However, before dying Zhao She had told his wife to warn the King not to appoint his son. He believed that Zhao Kuo was not a suitable general for the army as, although he had read the necessary classics, he had no actual experience. His wife did tell the King, but Zhao She said what the King wanted to hear, that he would engage the Qin army in direct conflict and end the stalemate and so the King ignored the wife's pleas and placed Zhao She in charge. Unfortunately for Zhao She the Qin general had also been replaced by the formidable Bai Qi. Soon after his appointment Zhao She led the Zhao army into a head on, tactless, attack on the Qin army. Bai Qi use the Cannae maneuver and surrounded the Zhao army whereupon he simply waited for the Zhao army to starve. The Zhao army tried to break through Qin lines on a couple of occasions and in the last attempt Zhao She was killed. Eventually the Zhao soldiers were capture and buried alive apart from 240 of the youngest soldiers who were freed to spread the word of what had happened.
http://en.wikipedia.org/wiki/Battle_of_Cannae - this should explain what the Cannae maneuver is if you are interested.