My brothers (and sisters) today is Saint Crispin's Day. The Battle of Agincourt was one of the greatest English victories in the Hundred Years' War. It falls on 25 October and is the feast day of the Christian saints Crispin and Crispinian (also known as Crispinus and Crispianus, though this spelling has fallen out of favor), twins who were martyred c. 286.
The Band of Brothers (related to title from the HBO series) speech about that battle is famous from Shakespeare's Henry V.
The Battle took place on 25 October 1415 (Saint Crispin's Day) near Azincourt in northern France. England's unexpected victory against a numerically superior French army boosted English morale and prestige, crippled France, and started a new period of English dominance in the war.