Hi, josepp, interesting thread. I do think that you might not be right about magister/magistrate. Magister is a pair with minister, and both prefixes are to do with size or status. A minister was originally a servant(and jolly well should remember it), while the greater (magna) person was the master.

Wich and wick had to do with trade in some cases - some are salt sources. A port or market, usually, or a manufacturing centre (Chiswick for cheese, eg). A few have been connected with Viking "vik", or inlet. I'm wondering which Sandwich is, being a major port in the early middle ages, but also a sandy inlet.

Though castra meant camp, not all places with the element were Roman forts. Rochester in Kent was a city retaining its Roman walls, as was Gloucester. The English were free with their definitions, and did not distinguish forts and cities.

Penny