Boulogne - sur - Mer Boulogne - sur - Mer ( , Latin : " Bononia " , ) is a city in northern France . It is a sub - prefecture of the department of Pas - de - Calais . Boulogne lies on the Côte d ' Opale , a touristic coast on the English Channel , and is the most - visited location in its region after the Lille conurbation . Boulogne is its department ' s second - largest city after Calais , and the 59th largest in France . It is also the country ' s largest fishing port , specialising in herring . Boulogne was founded during the Roman occupation of France , and as " Portus Itius " , was used for trade and conquest of Great Britain . After a period of Germanic presence following the collapse of the Empire , Boulogne was at the centre of an eponymous county of the Kingdom of France during the Middle Ages , and was occupied by the Kingdom of England numerous times due to conflict between the two nations . The city ' s 12th - century belfry is recognised by UNESCO as a World Heritage Site , while another popular attraction is the marine conservation centre , Nausicaa . Name . The name Boulogne was first recorded during the Roman Empire as " Bononia " , possibly a derivative of the root found in the Celtic word " bona " meaning " foundation " , " settlement " , " citadel " , and also found in Vindobona , the Roman name for Vienna . A " bona " was probably a granary . This derivation is also found in the name of the Italian city of Bologna . This city was founded by the Celtic Boii . The French suffix " - sur - Mer " is the direct equivalent of the English " - on - Sea " . History . Origin of the city . Originally named " Gesoriacum " and probably also to be identified with Portus Itius , by the 4th century Boulogne was known to the Romans as " Bononia " and served as the major port connecting the rest of the empire to Britain . The emperor Claudius used this town as his base for the Roman invasion of Britain , in AD 43 , and until 296 it was the base of the naval fleet of the " Classis Britannica " . Zosimus called the city " germanorum " , Germanic speaking , at the end of the 4th century . The city was an important town of the Morini . Middle Ages . In the Middle Ages Boulogne was the capital of an eponymous county , founded in the mid - 9th century . An important Count , Eustace II , assisted William the Conquerer in his conquest of England . His wife founded the city ' s Notre Dame cathedral , which became a site of pilgrimage from the 12th century onwards , attended by fourteen French kings and five of England . The city survived on herring fishing and received its municipal charter from Count Renaud of Dammartin in 1203 . The area was fought over by the French and the English , including several English occupations during the course of the Hundred Years War . Boulogne was again occupied by the English from 1544 to 1550 . In 1550 , The Peace of Boulogne ended the war of England with Scotland and France . France bought back Boulogne for 400 , 000 crowns . A culture of smuggling was present in the city until 1659 , when French gains in Flanders from the Treaty of the Pyrenees moved the border northwards . The Napoleonic period . Boulogne received its current status as a subprefecture of the Pas - de - Calais department in 1800 due to the territorial re - organisation in Revolutionary France . Three years later , it was given the title of an Imperial City " ( Ville Impériale ) " . The 19th century was a prosperous one for Boulogne , which became a bathing resort for wealthy Parisians after the completion of a railway line to the French capital . In the 19th century , the Basilica of Notre - Dame de Boulogne was reconstructed by the priest Benoit Haffreingue , who claimed to have received a call from God to reconstruct the town ' s ruined basilica . During the Napoleonic Wars , Napoleon amassed La Grande Armée in Boulogne to invade the United Kingdom in 1805 . However , his plans were halted by other European matters and the supremacy of the Royal Navy ( including thousands of Congreve rocket s ) . A nephew of Bonaparte , Louis - Napoleon Bonaparte , later Napoleon III , returned to France in secret from his exile in England , passing through Boulogne in August 1840 . He was later jailed for trying to lead a revolt in Strasbourg . The two world wars . During the First World War , this was the debarkation port for the first unit of the British Expeditionary Force to land in France , and for many others thereafter . It also was the site of an Allied ( French and British ) armaments production conference . On 22 May 1940 during the Battle of France , two British Guards battalions and some pioneers attempted to defend Bolougne against an attack by the German 2nd Panzer Division . Despite fierce fighting , the British were overwhelmed and the survivors were evacuated by Royal Navy destroyers while under direct German gunfire . On June 15 , 1944 , 297 planes ( 155 Avro Lancaster s , 130 Handley Page Halifax es , and 12 De Havilland Mosquito s ) of the Royal Air Force bombed Boulogne harbour to suppress German naval activity following D - Day . Some of the Lancasters carried Tallboy bomb s , and as a result , the harbour and the surrounding area were completely destroyed . In August , 1944 the town was declared a " fortress " by Adolf Hitler , but it succumbed to assault and liberation by the 3rd Canadian Infantry Division in September . In one incident , a French civilian guided the Canadians to a " secret passage " leading into the walled old town and by - passing the German defenders . To replace the destroyed urban infrastructure , affordable housing and public facility projects in functional , brutalist building styles were carried out in the 1950s and 60s . The harbour , therefore , is not typical of a northern French harbour . Sights . Boulogne ' s 12th - century Belfry is one of 56 in northeastern France and Belgium with shared World Heritage Site status . It is the oldest building in the upper city , and currently serves as the home to a museum of Celtic remains from the Roman occupation . Founded as the Counts ' dungeon , the top floor was added in the 13th century . Damage by a fire in 1712 was built over by 1734 . Official website : Tourism in Boulogne sur Mer Official website : Tourism in Boulogne sur Mer and the Boulonnais region Economy . Boulogne - sur - Mer is an important fishing port , with 7 , 000 inhabitants deriving part , or all , of their livelihoods from fishing . IFREMER ( the French Research Institute for Exploitation of the Sea ) and the Pasteur Institute are located in Boulogne Port . Certain brands , including Crown and Findus , are based in Boulogne Events . In the year 1905 the First Esperanto Universal Congress was held in Boulogne - sur - Mer . L . L . Zamenhof , the creator of Esperanto , was among the attendees . In the 2005 , there was a grand anniversary meeting , to mark the centenary , with more than 500 attendees . Education . Boulogne - sur - Mer hosts one of the oldest " Universités de l ' été " - summer courses in French language and culture . The Saint - Louis building of the University of the Côte d ' Opale ' s Boulogne campus opened its doors in 1991 , on the site of the former St . Louis hospital , the front entrance to which remains a predominant architectural feature . Its 6 major specialisms are Modern Languages , French Literature , Sport , Law , History and Economics . The University is situated in the town centre , about 5 minutes from the Boulogne Tintelleries train station . Health . Two health centres are located in Boulogne , the public Hospital Duchenne and the private Clinique de la côte d ' opale . Sports . Boulogne ' s football club , US Boulogne Côte d ' Opale ( US refers to Union Sportive ) , is one of the oldest in France due to the city ' s proximity to England , founded in 1898 . The club currently play in the third tier , the Championnat National , and host home matches at the 14 , 500 - capacity Stade de la Libération . Boulogne native and FIFA World Cup finalist Franck Ribéry began his career at the club . Basketball teams in Boulogne include Stade Olympique Maritime Boulonnais of the Nationale 1 and ESSM of Pro B . Culture . Food . As an international maritime port on the English Channel ( " La Manche " ) , the town of Boulogne - sur - Mer has European and American influences in local cuisine . They include : International relations . Twin towns — Sister cities . Boulogne - sur - Mer is twinned with :