Traiectum (Utrecht)
Traiectum ('ford') was founded in the mid-first century, probably by the Roman general Gnaeus Domitius Corbulo, governor of Germania Inferior in 47, although a slightly earlier date becomes increasingly likely now that other forts along the Lower Rhine (e.g., Woerden) have been dated to 40 or 41, when the emperor Caligula paid a visit to Germania Inferior. The small fort was situated on what is now called the Domplein, and is still the center of Utrecht.
The "treasure of the Domplein" (or what remains of it, since most coins were stolen)
Like all forts along the Lower-Rhine, Traiectum was destroyed during the Batavian revolt. An interesting discovery in this context was a treasure of fifty gold pieces found in an officer's house, buried by a centurio who was never able to find his coins back.
Between 88/89 and 260, it was garrisoned by the Second cohort of Spanish foot soldiers (cohors II Hispanorum peditata). The fort was enlarged and rebuilt from brick and natural stone in c.210. The wall was almost a meter wide. The castle was still functioning in the fourth century.
During the early Middle Ages, the Northumbrian monk Willibrord (668-739) visited Utrecht, and with authorization from the Franconian leader Pepin and pope Sergius III, built a church inside the ancient fort (695). This was the center of Christianity for the people called 'Frisians', i.e., all inhabitants of the area north of the Rhine.
A satellite photo can be found here.