On August 19th 1252 Birger Jarl, the then mightiest man in Sweden, sent a letter from "Stockholm". That was the first time the name was used in writing, and the first known date in the history of the city. Birger Jarl told peasants outside of Stockholm that they would have to pay taxes to the church - the so-called "tithe". The letter is preserved in the Swedish National Archives.
But what does "Stockholm" mean? Well, there is no simple answer. A legend tells of pirates who burnt the town of Sigtuna in the end of the 12th century, and that the inhabitants there rescued their valuables in a hollow log - the name for "log" in Swedish is "stock". Where the log reached land their new town was founded, and given the name "Stockholm". The medieval merchants called the town "Holm", which in latin became "Holmia". The most probable explanation, though, is that the name came from the poles - "stockar" - which were put in the water outside of the island to stop hostile enemies from entering.
For those who lived here, Stockholm was for a long time simply called "Staden" - "the Town".
Photo Stockholm-Storkyrkan 01by Jürgen Howaldtis licensed underCC BY-SA 2.0