The first settlements in this area have their origin 15 000 years ago (The picture shows excavations near the town).
The first written document mentioning the town ("Odeslo") is dated from 1151
1371 the town got the privilege as a marketplace.
At that time Oldesloe was a very important town and had 1500 inhabitants (for comparison: the largest Hanseatic-City Lübeck had 9000 and nearby Hamburg 5000 citizens). 60% of the east-west-trade of those days of the
Hanseatic League had to pass Oldesloe (a harbour on the Trave-river provided the possibility of shipping the goods to the Hanseatic-Metropole Lübeck)
More informatio (in German) you can get from
this site or you visit the Bad Oldesloe museum
here