Before the counts there was the pagus Bononiensis - the Frankish administrative district named for the Roman town of Bononia, the modern Boulogne-sur-Mer. Records before the eleventh century are thin. A ninth-century count named Herrequin appears in chronicles as a proverbial villain, though he may be folklore. By the late ninth century the region had come under the counts of Flanders. In 886, bishop Gauzlin of Paris asked count Erkenger of Boulogne to summon German help against Viking raids; Erkenger lost his possessions a decade later for backing the wrong Carolingian king. Out of these long-forgotten succession crises, somewhere around 1000, a distinct House of Boulogne emerged - small, strategically placed, and ambitious.

Eustace II of Boulogne fought beside William the Conqueror at Hastings in 1066. The Bayeux Tapestry shows him - or someone who must be him - pointing at William with his standard bearer in the thick of the fight. He had political reasons to back the duke: his first wife Goda was the half-sister of the dead king Edward the Confessor. Eustace's reward in England was vast - lands across more than a dozen English counties, making the count of Boulogne briefly one of the wealthiest landlords in the new kingdom. His descendants would marry into the English royal family. His granddaughter Matilda of Boulogne became queen consort of England in 1135 - she ran an effective war against the empress Matilda, her cousin, while her husband Stephen sat as king of England.

Eustace II's grandsons made the count of Boulogne a household name across Latin Christendom. Eustace III of Boulogne, the eldest, joined the First Crusade in 1096 with his two younger brothers, Godfrey of Bouillon and Baldwin of Boulogne. When Jerusalem fell to the Crusaders in 1099, Godfrey was elected the first Latin ruler of the city. He refused to wear a crown where Christ had worn thorns, and took the title Advocate of the Holy Sepulchre. He died within a year. His brother Baldwin succeeded him - this time as a crowned king, Baldwin I of Jerusalem - and ruled until 1118. Eustace III himself was later offered the throne and declined. Three brothers from a small French port, two of them rulers of the Holy City: an outcome no one could have predicted from the genealogies of 1050.

The county's independence ended on a July afternoon in 1214. Count Renaud of Boulogne had thrown in his lot with the imperial coalition against King Philip II of France. At Bouvines, near Tournai, Philip's army routed the imperials in one of the decisive battles of medieval Europe. Renaud was captured, lost his county, and died in royal prison. Philip II handed Boulogne to his own son, Philippe Hurepel, in 1223. After Hurepel's death the county passed through complicated marriages - his widow Matilda married Alphonse of Portugal in 1238, who divorced her in 1253 and became King Afonso III; the county went to her niece Adelaide of Brabant and to her husband William X of Auvergne; from there it descended through the La Tour d'Auvergne family for two more centuries.

The final heiress of medieval Boulogne was, of all people, the queen of France. Madeleine de la Tour d'Auvergne - granddaughter of the last medieval count - married Lorenzo II de' Medici, ruler of Florence, in 1518. Their daughter, Catherine de' Medici, would marry the future king Henry II of France and become one of the most powerful queens consort in European history. When Catherine's childless aunt Anne died in 1524, the counties of Auvergne and Boulogne passed to her. The medieval county had already lost its political distinctness - in 1477 Louis XI had absorbed it into the royal domain by swapping it for the county of Lauragais - but the bloodline of Eustace II of Boulogne ran straight through Catherine de' Medici and on into half the royal houses of seventeenth-century Europe. Not bad for a French pagus that began in shadowy ninth-century chronicles.