There were different battles at the battle of philippi.

In antiquity, there were other dates. On September 25, 480 BC the battle of Salamis in Greece took place. In this naval battle the Greeks stopped the Persian advance into Europe. The Great Siege of Malta ended on September 8, 1565. The Ottoman’s were finally driven from the island at St. Paul's Bay on September 11 of that year. The 8th is the Festival of Santa Maria because according to church tradition, the virgin Mary was born on that date. The lifting of the siege prevented the Ottoman’s from penetrating into Europe. The Moslem siege of Vienna was lifted on Sept. 11, 1683 by a combined army of Polish, German and Austrians soldiers led by a Polish king, Jan Sobieski, whom the pope and European leaders hailed as the "Savior of Western Civilization." This was the furthest the Ottoman’s were able to penetrate into Europe from the east. Of course, September 11, 2001 changed the world as we know it. Moslems have long memories and dates are important! September 11, 2001 was like saying: “We’re just picking up where we left off!” Date In the year 42 BC, the month of October was a pivotal month in the history of Western Civilization. Two large Roman armies were amassed against each other on the plains to the west of the ancient city of Philippi in Macedonia. One army was led by the Liberators, Brutus and Cassius, and the other army was led by Mark Antony and Octavian, later to be known as Caesar Augustus. What was at stake in this conflict was which direction the Roman Republic would take. Dio Cassius (AD 150-235) pointed out: “Now as never before liberty and popular government were the issues of the struggle.  … One side was trying to lead them to autocracy, the other side to self-government” (Roman History47.39.2; LCL 5: 197).

4.a depression is the answer