Utrecht:

In 1528 the bishop lost secular power over both Neder- and Oversticht – which included the city of Utrecht – to Charles V, Holy Roman Emperor. Charles V combined the Seventeen Provinces (the current Benelux and the northern parts of France) as a personal union. This ended the prince-bishopric Utrecht, as the secular rule was now the lordship of Utrecht, with the religious power remaining with the bishop, although Charles V had gained the right to appoint new bishops. In 1559 the bishopric of Utrecht was raised to archbishopric to make it the religious center of the Northern ecclesiastical province in the Seventeen provinces.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What was the religious center of Norther Europe?
unanswerable