During the Revolution, the old districts of Paris were grouped into ten or so departments. With the annexation of the neighbouring communes in 1860, the enlarged city was divided into twenty arrondissements distributed around the Seine. Their numbering started from the historic heart of the city, on the right bank, for the first four arrondissements, then crossed the Seine in a clockwise direction for the 5th, 6th, and 7th; it returns to the right bank for the 8th, 9th, 10th, 11th, and 12th, before switching back to the left bank for the 13th, 14th, and 15th, and ending on the right bank with the 16th, 17th, 18th, 19th, and 20th arrondissements.