Alsborg was built whilst the Wends still dominated the Danish coast; its location a few kilometers inland meant that the castle could not be attacked without warning, and the local population had a better chance of taking refuge there.
Alsborg blev bygget mens Venderne endnu hærgede de danske kyster, og placeringen nogle kilometer inde i land betød at borgen ikke kunne overfaldes uden varsel, og lokalbefolkningen fik bedre muligheder for at søge tilflugt i borgen.