Arras can be visited year-round. The main square is most attractive in spring and summer when the terrace cafes fill up and the Saturday market is at its busiest. July brings the Main Square Festival, one of the larger outdoor music events in northern France, which takes over the Grand'Place for a weekend.
The WWI memorial sites around Arras are busiest in spring and autumn when battlefield tourism is at its peak — school groups from Britain come in large numbers in May and June, and there is a particular focus around 11 November. For anyone visiting the battlefields, a weekday visit is more reflective than a weekend one. The underground sites (Les Boves and Carrière Wellington) are comfortable year-round at a constant cool temperature regardless of the weather outside.