The history of Gembloux goes back a very long way. The place name seems to point to the locality's Celtic origin. Traces of the Gallo-Roman era have been found in Gembloux along the Bavay Cologne Roman road crossing the city. The road connected the Channel to the Rhine via its extensions and was thus of huge importance in strategic, commercial and civilising terms. Its presence promoted the emergence of villas (farms) close to its path. Subsequent to a time of prosperity in the 2nd century, in common with the neighbouring regions, Gembloux had to contend with the Germanic invasions. These incursions were so violent that the inhabitants were compelled to leave the Roman road's surrounding areas and seek protection in the hinterland. This resulted in people settling on the rocky promontory where the historical centre of Gembloux is located. A Merovingian tomb (7th century) was discovered there, in 1935, during excavation works for creating new buildings for the current Faculty of Agricultural Sciences.
In the 10th century, the knight Wicbertus, who was canonised in 1110 as St. Guibert, created a Benedictine abbey in Gembloux and donated his personal possessions to the establishment.
This monastery was the powerhouse of local cultural and economic development during the 11th century. Abbot Olbert built the convent buildings and abbatial church in the Roman style.
The 12th century was a disaster for Gembloux. The small town was incorporated into the duchy of Brabant but at the border of the earldom of Namur. These two principalities were major rivals. Troops from the earldom of Namur launched several attacks on Gembloux during the 12th century, leaving the town devastated. The town was allowed to erect ramparts in1153 covering a surface area of roughly seven hectares. The abbey occupied three of the hectares. These ramparts with their four gates were flanked by several towers and lined ditches.
Subsequent to the Burgundian unification towards 1430, Gembloux lost its reputation of being a dangerous borderline town.
During the second half of the 16th century, Gembloux was caught up in the religious wars of that epoch and was even the scene of the battle, on 31 January 1578, between the army of the States, the Gueux (a league of Flemish and Dutch patriots formed to resist the introduction of the Spanish inquisition in the Netherlands), and Spanish troops led by the natural son of Charles the Fifth, Don Juan of Austria.
The abbot of the Gembloux Benedictine monastery was promoted successively to become the Ducal adviser, first noble of Brabant and in the mid-sixteenth century was granted the high office of earl. A jurisdictional lord invested with judicial powers the abbot exercised his privileges within the Gembloux region, which apart from the town included Cortil, Ernage, Grand-Manil, Bertinchamps, part of Lonzée, and Sauvenière Liroux. The abbot was required every year to appoint the mayor and aldermen, who could also be removed by him at any time. Under the Ancien Regime, Gembloux was under the abbot's sway thus barred from asserting itself as an autonomous town. The abbey assumed the political role that the town had begun to play during the 12th and 13th centuries.
As a result of the wars Louis XIV waged in our provinces Gembloux continued along its path to ruination.
6 August 1678 is the date of a huge fire that accidently broke out, devastating the town. Not until the second half of the 18th century did Gembloux begin to enjoy a period of comparative prosperity. The cutlery industry sprang up during that time and this development meant the market town would lose its character as an area devoted exclusively to farming. The monastic buildings and the abbey church, originating in the 11th century, then became obsolete. The rebuilding work required got underway at the end of Eugene Gerard's abbacy (1739-1758) and mainly continued under abbot Jacques Legrain (1759-1790), who called on the services of the famous architect Laurent Benoît Dewez. The abbey rebuilding programme drew to a close in 1779.
Nonetheless, the monks lived in their new building for only very short time. The French Revolution, the revolutionary troops' incursion into the Austrian Netherlands and their annexation to France in 1795 dealt the death blow to the Ancien Regime and its archaic structures. The earldom of Gembloux was dissolved, so the French succeeded in ending Gembloux's inclusion in the Brabant sphere of influence. The town therefore became a municipality of the department of Sambre-Meuse. The French Director also called for the religious orders to be abolished and their possessions to be confiscated in the name of the Republic. Gembloux abbey was eradicated and its possessions disposed of in 1797. The old abbey estate was bought by a French businessman, Jean-Baptiste Paulée. The abbey estate's religious purpose thus drew to a close. Pursuant to an imperial decree of 1810, the municipalities of Gembloux, Grand-Manil and Lonzée were allowed to acquire the former Gembloux abbey to replace the dilapidated St. Sauveur parish church whose foundations dated from the 10th century. During the Battle of Waterloo, in June 1815, troops passed through Gembloux several times or were quartered there.
In 1830, several Gembloux citizens participated in the "Days of September", the conflicts to gain Belgian independence. Gembloux was connected by rail to Brussels in 1855 in Namur and the following year.