The former French diocese of Thérouanne (Lat. Moriniensis or Taruannensis) controlled a large part of the left bank of the river Scheldt during the Middle Ages. Territorially it was part of the county of Artois which belonged to the county of Flanders.
In the 7th century, probably around 639, Saint Audomar (Saint Omer) established the bishopric of Terwaan or Terenburg in Thérouanne. Thanks to that ecclesiastical control of some of the most prosperous cities north of the Alps, like Arras and Ypres, the bishopric was able to build a cathedral which was at the time the largest in France.
In 1553 Charles V besieged Thérouanne, then a French enclave in the Holy Roman Empire, in revenge for a defeat by the French at Metz. After he captured the city he ordered it to be razed to the ground and the roads to be broken up. In 1557, as a result of the war damage to its see, the diocese was abolished. About two decades later the diocese of Boulogne was created, bearing the name Thérouanne for a few years.
The disappearance of the former bishopric led to a reform of sees at the Council of Trent, and the bishopric of Thérouanne was split between the Diocese of Saint-Omer, the diocese of Boulogne and the Diocese of Ypres.
Before 639, to c. 667 (†): Audomar (Omer)
c. 667 to c. 669/701:Bainus
c. 669/701 to c. 721/723: Ravengerus
Pas-de-Calais / medieval archdiocese of Reims
Thérouanne Cathedral is generally forgotten in art-historical surveys as it was demolished not in the Revolution, but at the surprisingly early date of 1553, along with… its entire city. However, there is a remarkable amount of visual material for it from its final few decades, and some archaeological evidence too.https://en.m.wikipedia.org/wiki/Ancient_Diocese_of_Thérouanne
Saint-Omer (French pronunciation: [sɛ̃t‿ɔmɛʁ]; West Flemish: Sint-Omaars) is a commune in France.
Saint-Omer first appeared in the writings during the 7th century under the name of Sithiu (Sithieu or Sitdiu), around the Saint-Bertin abbey founded on the initiative of Audomar, Odemaars or Omer).
Omer, bishop of Thérouanne, in the 7th century established the Abbey of Saint Bertin, from which that of Notre-Dame was an offshoot. Rivalry and dissension, which lasted till the French Revolution, soon sprang up between the two monasteries, becoming especially virulent when in 1559 St Omer became a bishopric and Notre-Dame was raised to the rank of cathedral.
In the 9th century, the village that grew up round the monasteries took the name of St Omer. The Normans laid the place waste about 860 and 880. Ten years later the town and monastery had built fortified walls and were safe from their attack. Situated on the borders of territories frequently disputed by French, Flemish, English and Spaniards, St Omer for most of its history continued to be subject to sieges and military invasions.
In 932 Arnulf of Flanders conquered the County of Artois and Saint-Omer (Sint-Omaars in Dutch) became part of the County of Flanders for the next three centuries. In 1071 Philip I and the teenage Count Arnulf III of Flanders were defeated at St Omer by Arnulf's uncle and former protector, Robert the Frisian, who subsequently became the Count of Flanders until his death in 1093.
Along with its textile industry, St-Omer flourished in the 12th and 13th century. In 1127 the town received a communal charter from the count, William Clito, becoming the first town in West Flanders with city rights. Later on the city lost its leading position in the textile industry to Brugge. After the mysterious death of Count Baldwin I, the County of Flanders was weakened. In 1214 Philip II of France captured Baldwin's daughter Joan and her husband Ferdinand, Count of Flanders and forced them to sign the Treaty of Pont-à-Vendin, in which Artois was yielded to France. Ferdinand did not take this lying down, and allied with Emperor Otto IV and John, King of England, he battled Philip II at Bouvines, but was defeated. Despite the political separation for the next 170 years, the city remained part of the economic network of Flanders.
In 1340 a large battle was fought in the town's suburbs between an Anglo-Flemish army and a French one under Eudes IV, Duke of Burgundy, in which the Anglo-Flemish force was forced to withdraw. From 1384, St-Omer was part of the Burgundian Netherlands, from 1482 of the Habsburg Netherlands and from 1581 to 1678 of the Spanish Netherlands.
The French made futile attempts against the town between 1551 and 1596. During the Thirty Years' War, the French attacked in 1638 (under Cardinal Richelieu) and again in 1647. Finally in 1677, after a seventeen-day siege, Louis XIV forced the town to capitulate. The peace of Nijmegen signed in the fall of 1678 permanently confirmed the conquest and its annexation by France. In 1711, St-Omer was besieged by the Duke of Marlborough. On the verge of surrendering because of famine, Jacqueline Robin risked her life to bring provisions into the town, in memory of which in 1884 a large statue of her was erected in front of the cathedral.
The College of Saint Omer was established in 1593 by Fr Robert Persons SJ, an English Jesuit, to educate English Catholics. After the Protestant Reformation, England had established penal laws against Catholic education in the country. The college operated in St Omer until 1762, when it migrated to Bruges and then to Liège in 1773. It finally moved to England in 1794, settling at Stonyhurst, Lancashire. Former students of the College of Saint Omer include John Carroll, his brother Daniel and his cousin Charles.
During World War I on 8 October 1914, the British Royal Flying Corps (RFC) arrived in Saint-Omer and a headquarters was established at the aerodrome next to the local race course. For the following four years, Saint-Omer was a focal point for all RFC operations in the field. Although most squadrons only used Saint-Omer as a transit camp before moving on to other locations, the base grew in importance as it increased its logistic support to the RFC. Many Royal Air Force squadrons can trace their roots to formation at Saint-Omer during this period. Among which are No. IX Squadron RAF which was formed at Saint-Omer, 14 December 1914 and No. 16 Squadron RAF which was formed on 10 February 1915.
During World War II, the Luftwaffe used the airfield. When the RAF's legless Battle of Britain ace, Douglas Bader, parachuted from his Spitfire during an aerial battle over France, he was initially treated at a Luftwaffe hospital at Saint-Omer. He had lost an artificial leg when bailing out, and the RAF dropped him another one during a bombing raid.https://en.m.wikipedia.org/wiki/Saint-Omerhttps://en.m.wikipedia.org/wiki/Saint-Omer_Cathedral