Before 1860, Paris was divided into 12 «Arrondissements» (districts) numbered from west to east on each bank of the river.
Then Emperor Napoleon III (1852-1870) decided to expand the city limits and divide it into 20 districts. It was originally planned to give additional numbers to the newly integrated areas with the new Arrondissement west of the first district becoming the "13th" district. Oh, but that was not at all agreeable to the wealthy people who lived in the former village of Passy! At the time there was a saying in France that people used when referring to a « shameful » unmarried couple: « they got married in the 13th district » (like they could have said "they got married on the 32nd of the month"). So it was then decided to renumber all the districts of Paris in a spiral fashion starting with the Louvre (the Imperial Palace at the time) as number one.
Thus, we inherited this « snail shell » layout that we still use to this day !
Paris (red contour) + close suburbs