How was bacchanalia held?

Every time grapes are harvested, juiced, new wine is opened, and business transactions are held, people will hold Dionysus-related sacrificial activities as many as four times a year. Among them, bacchanalia, the city held in March and April every year, is the most grand. 10 city-state centered on Athens. Five people in each group formed a choir of 50 people and sang hymns around the altar of Dionysus.

Rubens' oil painting bacchanalia.