Earths magnetic field over the last 1000 years To investigate the reliability and stability of spherical harmonic models based on archeo paleomagnetic data 2000 Geomagnetic models were calculated. All models are based on the same data set but with randomized uncertainties. Comparison of these models to the geomagnetic field model gufm1 showed that large scale magnetic field structures up to spherical harmonic degree 4 are stable throughout all models. Through a ranking of all models by comparing the dipole coefficients to gufm1 more realistic uncertainty estimates were derived than the authors of the data provide. The derived uncertainty estimates were used in further modelling which combines archeo paleomagnetic and historical data. The huge difference in data count accuracy and coverage of these two very different data sources made it necessary to introduce a time dependent spatial damping which was constructed to constrain the spatial complexity of the model. Finally 501 models were calculated by considering that each data point is a Gaussian random variable whose ...