Aker was a former independent municipality in Akershus, Norway, that constitutes the vast majority of the territory of the modern city of Oslo.
The name originally belonged to a farm which was located near the current Old Aker Church.
The first expansion came as early as 1629, when a number of farms were transferred into the Bymarken area of the city.
Bymarken was a commons in which citizens could engage in agriculture to their own housekeeping, and provide summer and winter fodder for livestock.
Bymarken lay under the city's civil administration, but for ecclesiastical purposes remained part of Aker's parish.