Citadel of Doullens, Military citadel in Doullens, France.

The Citadel of Doullens is a Renaissance fortification on an irregular pentagon plan at the confluence of the Grouche and Authie. Its oldest part, built from 1530 under Francis I, is a four-bastion stone fortress with orillons and casemated flanks. In 1599 Jean Errard added a second line of three brick bastions with stone quoins in front of the south-west front. Parts of the site are ruined.

François I had a sandstone citadel built at Doullens from 1530, entrusted to Robert Mailly, with four bastions with orillons and casemated flanks. In 1599 Henri IV had Jean Errard add a second line of three brick bastions with stone quoins on the south-west front. The Treaty of the Pyrenees in 1659 ended its military role and it became a place of detention.

Since 1987 the citadel has hosted the Fête des Plantes du Nord de la France, a plant fair held regularly within the walls. The site opened to the public in 1982, after the association Les Amis de la Citadelle was founded in 1974 and the département bought the fortress in 1978.

The citadel stands at the confluence of the Grouche and Authie on the edge of Doullens, and parts of the five-sided enceinte are in ruins, so watch your footing on uneven ground. It has been open to the public since 1982. The site is large; allow time to walk between the bastions and the inner four-bastion core.

Since 1987 the Fête des Plantes du Nord de la France has been held regularly in the citadel, drawing nursery growers who display their plants within the old walls. The site had been abandoned from 1963 and was bought by the Département in 1978, then opened to the public in 1982.