Rudolf Simek

“Nine is the mythical number of the Germanic tribes. Documentation for the significance of the number nine is found in both myth and cult. In Odin's self-sacrifice he hung for nine nights on the windy tree (Hávamál), there are nine worlds to Nifhel (Vafprudnismal 43), Heimdallr was born to nine mothers, Freyr had to wait for nine nights for his marriage to Gerd (Skírnismál 41), and eight nights (= nine days?) was the time of betrothal given also in the Þrymskviða. Literary embellishments in the Eddas similarly used the number nine: Skaði and Njörðr lived alternately for nine days in Nóatún and in Þrymheimr; every ninth night eight equally heavy rings drip from the ring Draupnir; Menglöð has nine maidens serve her (Fjölsvinnsmál 35ff), and Ægir had as many daughters. Thor can take nine steps at Ragnarök after his battle with the Midgard serpent before he falls down dead. Sacrificial feasts lasting nine days are mentioned for both Uppsala and Lejre and at these supposedly nine victims were sacrificed each day.”
― Rudolf Simek, A Dictionary of Northern Mythology