What was the bloodiest battle in Roman history?

In 113 BC, a large Germanic-Celtic alliance began to wander around Rome. They crushed the Roman army and sent the Romans into panic. This army had two hundred thousand men, how could Rome possibly resist.

Enter this step, Caesar's uncle Marius. Marius was the most famous general of his time, and he began to rapidly reform the Roman army, creating more traditional Roman legions that we all know and love.

When this huge army began to move toward Italy, Marius responded with his Legion of Reform. What followed was a massive all-out conflict, with Roman discipline preventing an even larger army. A turning point occurred when a commander named Sula counterattacked the Celtic cavalry and asked them to flee to their own front.

Of all the Plutarch reports, 100,000 people were killed, Livy reported 160,000, and Orosius reported 140,000 killed.

Hannibal invaded Italy, and Rome responded by rallying the largest army in its history, an army of about 90,000 men. The Romans used this army to attack Hannibal, pushing their powerful heavy infantry forward through Hannibal's lines.

Hannibal cleverly made his flank stronger, so that when his center bent inward, his flank did not. This created a large "U" shape, and the Romans found themselves oppressed in all directions. Hannibal's cavalry then bypassed the rear and surrounded the entire Roman army. They then pressed in and killed about 50,000 Romans.