Outside the Vienna Secession building stands one of the more theatrical bronze monuments in Europe: the Marc Anton Gruppe, cast in 1899 by the Austrian sculptor Arthur Strasser. It shows Mark Antony in full Roman dress, seated in a chariot pulled not by horses but by four lions — two fully grown, two younger, all rendered with remarkable musculature and a controlled ferocity that has not softened in 125 years of Viennese weather. The patina has gone deep green. The lions look ready to move. Antony sits above them with the bearing of a man accustomed to commanding things that could kill him.

On August 9, 378 AD, the Eastern Roman emperor Valens led his army against a Gothic force near Adrianople in Thrace — modern Edirne in northwestern Turkey — and was killed along with roughly two-thirds of his army. The Battle of Adrianople was not the largest Roman defeat in history; Cannae killed more Romans in a single afternoon. It was not the most strategically complex engagement the Romans ever fought; the tactics were relatively straightforward. What made it consequential was not the battle itself but what came before it and what followed from it, the chain of decisions and consequences that makes Adrianople one of the pivots of late Roman history.

On August 2, 216 BC, on a flat plain near the Aufidus River in southern Italy, the Carthaginian general Hannibal Barca destroyed a Roman army of approximately 86,000 men in a single afternoon. Somewhere between 47,000 and 70,000 Romans died — the numbers vary by ancient source but the scale is not in dispute. It was the bloodiest day in Roman history, possibly the bloodiest single day of battle in the ancient world, and it accomplished nothing. Rome did not fall. It did not negotiate. It raised more legions and kept fighting.

On August 9, 48 BC — the same calendar date, by a coincidence historians have noted, as the Battle of Adrianople 426 years later — Julius Caesar’s army defeated Pompey’s at Pharsalus in Thessaly, ending the civil war between them in a single afternoon and ending the Roman Republic as a functioning political institution in any meaningful sense. The Republic would survive in form for another seventeen years, until Augustus completed its constitutional conversion. But Pharsalus was where it ended in fact, because Pharsalus eliminated the only man with the political authority, military reputation, and institutional support to contest Caesar’s supremacy on terms the existing system could legitimate.

In the autumn of 9 AD, three Roman legions — the Seventeenth, Eighteenth, and Nineteenth — were destroyed in the forests of Germania over the course of three days. The commander, Publius Quinctilius Varus, fell on his own sword. Approximately twenty thousand soldiers died. The eagle standards of all three legions were captured — the most significant military humiliation in Roman history, measured by what it did to the Roman strategic imagination. Augustus, reportedly, wandered through his palace for months afterward crying out for Varus to give him back his legions. Whether or not he actually said this, the story captures the psychological weight of what had happened.

The Battle of Zama in 202 BC ended the Second Punic War and established Roman dominance over the western Mediterranean for the next three centuries. It was the only battle Hannibal ever lost in a pitched field engagement, and it was lost to the one Roman general who had studied his methods carefully enough to use them against him. Scipio Africanus was thirty-four years old when he defeated Hannibal at Zama. He had spent his career learning from Carthage’s mistakes and Rome’s. The education was complete.