I remember reading about the systemic destruction of Mayan artefacts by the Catholic church including their codices*, but was this a generalised practice carried out in Europe, or just the new world? If so what were some of the most important artefacts to have been lost in this way?
*edit: codices is the plural of codex apparently...
The felling of the Donareiche (Thor's oak) in Germany by St Bonifatius comes to mind.
Follow up: Wikipedia says, many churches in Germany (Europe?) were simply built in place of older holy places (groves, Menhirs). How would this 'usually' happen during the christianization period? Were the people (forcefully?) converted and a church built there to prevent them from going back to their old gods? Or driven out and replaced with faithful christians? Or would a tribe leader express his submission under Frankish rule by building a church?
This isn't exactly the same, but there was the business with the Iconoclasts, who went around within the Eastern Church destroying anything that could be construed as a "graven image" - including likenesses and relics of the saints - partially as a response to Islamic bans on images, but also as a way to potentially gain Jewish and Muslim converts... or at least to bring the empire into accordance with the rules laid out in Exodus.
Byzantine Emperor Leo III was responsible for the peak of iconoclasm. Here, as described in the Catholic Encyclopedia:
In 726 Leo III published an edict declaring images to be idols, forbidden by Exodus 20:4-5, and commanding all such images in churches to be destroyed. At once the soldiers began to carry out his orders, whereby disturbances were provoked throughout the empire. There was a famous picture of Christ, called Christos antiphonetes, over the gate of the palace at Constantinople. The destruction of this picture provoked a serious riot among the people. Germanus, the patriarch, protested against the edict and appealed to the pope (729). But the emperor deposed him as a traitor (730) and had Anastasius (730-54), formerly syncellus of the patriarchal Court, and a willing instrument of the Government, appointed in his place. The most steadfast opponents of the Iconoclasts throughout this story were the monks. It is true that there were some who took the side of the emperor but as a body Eastern monasticism was steadfastly loyal to the old custom of the Church. Leo therefore joined with his Iconoclasm a fierce persecution of monasteries and eventually tried to suppress monasticism altogether.
A similar wave of iconoclasm followed during the Protestant Reformation around 700 years later.