In a medieval tower in the Tallinn Old Town wall there is a wooden internal door that was suspected of being rather old. The age of the door was determined using dendrochronology. It was possible to measure tree rings from the lower ends of the oak planks of the door. Matching the ring-width series with oak references from northern Europe revealed that the door was over 600 years old, and still in place in medieval Bremen Tower in Tallinn, Estonia. The ring-width series of the door was most similar to oak chronology from the Daugava River. However, this does not mean that the door timbers originate from that region. At present, we do not possess Estonian oak chronologies extending back to that time. Thus, the provenance of the oak for this door remains undecided. The dendrochronological date of the door, AD 1394–1411, can be confirmed and can be narrowed by documentary evidence to AD 1400–1410