Découvert en 1840, le site de Bougon a très tôt livré des éléments parlants – notamment un trésor de 200 squelettes humains et d’offrandes. Ce que l’on prenait pour des tas d’épierrements s’est révélé être une nécropole abritant plusieurs tumulus (dolmens recouverts d’un remblai), dont le département des Deux-Sèvres négocia l’acquisition en 1875.

                                                                                                                                                                                                                                                                                                                                                                                         Après un siècle d’interruption, les fouilles ont repris en 1968 et ont été dirigées de 1972 à 1985 par Jean-Pierre Mohen. Avec son équipe, celui-ci a recueilli 23 000 autres fragments d’os, appartenant à 110 adultes et 35 enfants.

                                                                                                                                                                                                                                                                                                                                                                                                                            Il a aussi avancé dans la reconnaissance et l’interprétation des six tumulus, qui ont été utilisés pendant plus de mille ans, à partir de 4700 avant J.-C.                                                                                                                                                                                                                                                                                                                                                                                              

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    Le tumulus le plus ancien possédait une coupole en pierre sèche, comme dans les trulli d’Italie du Sud. Le tumulus central avait une toute petite chambre tandis que le tumulus A, de forme circulaire, avait une dalle de 90 tonnes en aigrain, une pierre fossile d’origine corallienne. Quant au tumulus F, long de 72 mètres, il possédait deux chambres, une à chaque extrémité.

La variété des pierres utilisées imposait de déterminer leur provenance, dans une configuration géographique assez simple : un plateau encadré par deux rivières, la Sèvre niortaise et le Pamproux, la nécropole se trouvant à équidistance des deux.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               La conclusion fut que les pierres de la nécropole provenaient de différentes carrières, ce qui donnait l’impression que plusieurs communautés avaient choisi de réunir leurs morts en un même lieu, bien visible, sur une élévation de terrain.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                L’une des dalles de couverture pesait 90 tonnes, l’autre, près de 32 tonnes.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       Elle était constituée d’une roche dure - du calcaire bathonien à silex - provenant d’une carrière située à 4 kilomètres.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Comment les hommes préhistoriques s’y sont-ils pris pour déplacer de telles masses sur les tumulus ?

« Dans les années 1970, des observateurs avançaient que c’était un exploit impossible à réaliser par des hommes du néolithique, explique Jean-Pierre Mohen.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Certains “archéologues des forces secrètes” y voyaient l’action de puissances sidérales. 

                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Nous commencions à disposer d’éléments, provenant des fouilles, sur le type de pierre et d’outils utilisés, etc.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Il fallait tenter une démonstration pour prouver que cela était possible ! » L’extraction de la pierre ne pose pas de problème.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Les strates de la roche sont accentuées par percussion.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          On introduit des coins de bois mouillés et taillés en biseau et ainsi la roche finit par se « cliver » sans besoin de la tailler jusqu’au bout.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Elle est ensuite extraite grâce à des pics en bois de cerf. Mais pour le transport ? La réussite de l’opération, programmée pour l’été 1979, passait par la coopération des habitants.

« Je suis allé voir les maires en leur expliquant que nous faisions des fouilles depuis dix ans, que nous commencions à comprendre mais qu’il fallait vérifier les hypothèses, poursuit le préhistorien, qui avoue avoir rencontré un certain scepticisme.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    Bougon se trouve à côté de l’école d’officiers de Saint-Maixent, qui se sont rendus disponibles. Quand les maires l’ont appris, ils ont tout de suite accepté de nous aider ! Le Conseil général, propriétaire du site, a proposé de monter une buvette…

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Une scierie nous a fourni les troncs pour le roulement. Un vieux couple nous a indiqué les techniques ancestrales pour fabriquer des cordes en fibres de lierre et de viorne. »

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Tout est prêt pour l’épreuve le 28 juillet 1979. Cinq cents volontaires sont présents dès le lever du soleil.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    Empaquetée, encordée, progressant sur des « rouleaux » posés sur des « rails » (d’autres troncs équarris), la dalle tractée par 200 tireurs avance de plusieurs dizaines de mètres dans la matinée.