Here's a short story:

Although there is some evidence of earlier inhabitation in the region of Utrecht, dating back to the Stone Age (app. 2200 BCE) and settling in the Bronze Age (app. 1800–800 BCE), the founding date of the city is usually related to the construction of a Roman fortification (castellum), probably built in around 50 CE. A series of such fortresses was built after the Roman emperor Claudius decided the empire should not expand north. To consolidate the border the limes Germanicus defense line was constructed along the main branch of the river Rhine, which at that time flowed through a more northern bed compared to today (what is now the Kromme Rijn). These fortresses were designed to house a cohort of about 500 Roman soldiers. Near the fort settlements would grow housing artisans, traders and soldiers' wives and children. 

From the middle of the 3rd century Germanic tribes regularly invaded the Roman territories. Around 275 the Romans could no longer maintain the northern border and Utrecht was abandoned. Little is known about the next period 270–650. Utrecht is first spoken of again several centuries after the Romans left. Under the influence of the growing realms of the Franks, during Dagobert I's reign in the 7th century, a church was built within the walls of the Roman fortress. In ongoing border conflicts with the Frisians this first church was destroyed. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What is Utrecht's official found date?
Guess: 50 CE

Question: What two ages can it be traced back to?
Guess: Stone Age and Bronze Age

Question: Who decided not to grow northward?
Guess: Claudius

Question: What did he do to prevent this?
Guess: build fortresses

Question: When was the city eventually abandoned?
Guess: Around 275

Question: What was built under the Franks?
Guess: a church

Question: What eventually happened to it?
Guess: destroyed

Question: What caused it?
Guess: ongoing border conflicts

Now answer the following question in the same format.

Question: With whom?

the Frisians