The question "what happened in Arras" is a bit broad and can refer to different events that happened in Arras throughout history. However, based on the search results, it seems that the most significant event that happened in Arras was the Battle of Arras in 1917. Here are some key points about the battle:

• The Battle of Arras was a British offensive on the Western Front during World War I).
• The battle took place from April 9 to May 17, 1917.
• The British achieved the longest advance since trench warfare had begun, surpassing the record set by the French Sixth Army on July 1, 1916).
• The Canadian Corps was charged with taking Vimy Ridge, which was considered virtually impregnable, and they succeeded in capturing it.
• The British operations at Arras achieved impressive advances in the early stages, but the French action ended in catastrophe. Their struggle for the Chemin des Dames Ridge resulted in heavy casualties and proved so damaging to the armys morale that there were mutinies.
• The battle resulted in some 300,000 casualties.

Its worth noting that there was also a recent stabbing attack at a school in Arras in October 2023, which resulted in one death and two injuries. However, this event is not related to the Battle of Arras in 1917.