OK,
first of all historical army battle sizes and casualties are usually so different from source to source that it's impossible to successfully determine the more or less exact number. Have a look at the Polish-Swedish discussion for example ... The side that lost the battle most probably lowers the figures so that it doesn't look like a great defeat, whilst the winning size pushes enemy casualty figures / and army size to make it seem more of a great victory. It's the same for other conflicts.
I know of several huge battles, though my speciality is more in central / eastern Europe so I'll give you those figures.
1410 - Battle of Grunwald. Poles vs the Order. Figures are wild on casualties and numbers of this battle, though almost everyone agrees it was the largest battle in the medieval ages in the whole of Europe. Figures are from between 45,000 to >100,000 soldiers from both sides.
1610 - Klushino. Poles vs Muscovites (with mercenary support from the west). Poles had 9,000 men, the Muscovites around 30,000.
1651 - Beresteczko. Poles vs Cossack rebels with Tartar support. Apparently the largest cavalry battle of the 17th century. Poles had in excess of 45,000 men whilst many sources claim the Cossack side had over 100,000 men. Whatever is the fact, ppl are still discovering weapons and armour from the earth where the battle was thought even now.
1621 - Chocim1. Poles vs Turks. Poles had about 10-20,000 men. Turks were besieging the fortress .. figures are said to be anywhere from 50,000 to 100,000.
1673 - Chocim2. Poles vs Turks. Poles had between 20,000 and 40,000 men. The Turks apparently had between 80,000 and 120,000 men. This time it was the Poles time to charge into the fortress.
1683 - Relief of Vienna. Combined Polish/German force under Sobieski was about 45-50,000 men. Turks are said to have had a huge around exceeding 100,000 men.
Again, these figures should always been taken with a grain of salt, though they are more trusted if they are represented in several different historical sources. The above battles are some of the largest ones I can recall. Many of the larger ones the Poles fought against were usually hordes of Tartar cavalry, huge Turkish armies of janissaries and Turkish cavalry as well as huge mobs of Muscovite armies.
Sapura
[This message has been edited by Sapura (edited 26-07-2000).]