Complex sentence: Dies Sanguinis ("Day of Blood") was a festival held in Ancient Rome on 24 March, called Bellona's Day, when the Roman votaries of the war-goddess Bellona cut themselves and drank the sacrificial blood to propitiate the deity.
Split into simpler sentences: Dies Sanguinis ("Day of Blood") was a festival held in Ancient Rome on 24 March. Also known as Bellona's Day, this was an occasion when the Roman votaries of the war-goddess Bellona cut themselves and drank this sacrificial blood to propitiate the deity.