Fort de Valros The Fort de Valros ( also known locally as Tour de Valros ) is a ruined small castle or fortress in the " commune " of Valros in the Hérault " département " of France . In the mid - 19th century , the fort was the site of a semaphore station . History . The site has no visible trace of occupation from antiquity , but archaeological digs have uncovered the remains of a necropolis used from the 8th to the 10th century . The promontory on which the fort stands is a strategic observation post . At 100 m altitude , it dominates the valley of the Thongue and controls two very ancient communication routes : the roads from Béziers to Pézenas and from Saint - Thibéry to Alignan - du - Vent . From historical records , it is known that in 1199 , the powerful Viscount of Béziers , Raymond Roger Trencavel , authorised his vassal Etienne de Servian to build a " forcia " on the " podium " of Valros . But , from 1210 , during the Albigensian Crusade , Etienne de Servian was forced to recount , under pressure from the troops of Simon de Montfort . Thus , the fortress had only a short functioning military life . It was dismantled soon after its construction , in the first half of the 13th century . Thereafter , the site continued to be frequented by troops who took water from the cistern , which never dried up . Architecture . The fort was protectd externally by a dry moat and a first " enceinte " , the " braie " , defining a peripheral circuit , the " lice " . This " lice " was , in case of need , defended by a clever device of horizontal removable posts . In the north east corner of the " braie " , a broken stretch of wall suggests the location of the access bridge . The modern footbridge now stands there . The shortest distance from the bridge to the entrance to the fort obliged an assailant to go left along the wall , exposing his right side , the most vulnerable because not protected by armour . The fort itself , a 24 m square , has a wall 1 . 80 m thick with a single opening , in the south . Above this gate was a " hourd " , a kind of wooden hut , designed to allow firing down onto assailants . The holes for the supporting structure are still visible . The interior was occupied by lean - to buildings whose roofs fed a central cistern of approximately 40m capacity . The surrounding wall , which reached a height of at least 11 m , supported a round walk and , certainly , crenellation . To the left of the door , traces of projecting stones suggest the presence of a staircase giving access to the round walk . In the north east corner , opposite the bridge , stored stones are witness to a project to build a keep , never completed . Three materials were used in the construction . Basalt was used for the centre of the surrounding walls , all of the upper parts and for the external " enceinte " . The basalt came from the digging of the moat . Volcanic breccia , a conglomerate , was used for the parts of walls above a height of 7 m . This rock was taken from a quarry on the east flank of the hill . Limestone from Pézenas was used in the construction of the cistern and the entrance door . Telegraph tower . The small square tower nestled in the south west corner of the fortress ( number 7 on the plan above ) is a remnant of the aerial telegraphy invented at the end of the 18th century by the engineer Claude Chappe ( 1763 - 1805 ) , using semaphore signals . The first semaphore telegraphy line was established in 1794 between Paris and Lille . The French network extended over 5 , 000 km with 534 stations serving 29 towns . Installed in 1834 , the line linking Avignon to Narbonne , via Valros , was functioning until 1853 . The semaphore network was then replaced by electric telegraphy . The " tours de Chappe " ( Chappe towers ) , every 12 km or so , were built on high points . Each station was equipped with a mechanism for transmission and two telescopes to receive a message and to control its onward transmission . The mechanism consisted of a vertical mast supporting a 4 . 60 m long movable arm , the " regulateur " . At either end of the latter was a secondary arm , 2 m long , the " indicateurs " . The mast extended down into the interior of the tower into a tight room , 3 m by 3 m , sheltering the " stationnaire " , the solitary worker glued to his telescopes . For speed , and confidentiality , messages were encoded using a table where each figure signified a word or phrase . To transmit a message , the " regulateur " was placed either horizontally or vertically . The " indicateurs " were articulated every 45 , with 7 positions for each . This gave a total of 98 combinations ( 7 X 7 X 2 ) , of which six were reserved for the service - the only ones whose meanings were known to the " stationnaire " . The total repertoire of messages was , therefore , 92 pages of 92 lines , a total of 8 , 464 . Signals were sent in groups of two : the first number for the number of the page , the second for the number of the line on that page .