I was recently reading a small book called "The fortifications of Seligenstadt" (translated title).

Seligenstadt is a small town with the old town's centre very nicely preserved (the houses in the centre are several hundred years old) which is located south-east of Frankfurt, Germany.

The town was given by Charlemagne ("Karl der Große") to his councellor and biograph Einhard (also called Eginhard) as a gift. Einhard founded the monastery there and the town was part of it, in fact it even belonged to the monastery for a long time.

The small book was interesting for me to learn more about medieaval fortifications - of which some rests still can be see in situ in Seligenstadt itself, especially a few towers.

http://en.wikipedia.org/wiki/Seligenstadt (This is in English, and shows the monastery and the so-called "Einhardbasilika", the church in which relics of the holy Marcellinus and Peter are kept.)

If you use the google picture search with the town's name as a key word, you can see many more pictures about it.