The Fort de l'Olive is a fortification in the vicinity of Briançon in the Dauphiné region of southeastern France.
 Initially called the "Ouvrage du Bois des Gasquets", it was the third and final fort built near Briançon as part of the Séré de Rivières system of fortifications in the 1870s and 1880s.
 Located at an altitude of 2239 m , the fort overlooked the valley of the Clarée above the village of Plampinet from a height of 800 m with a view of the Italian frontier.
 It specifically controlled the Col de l'Echelle, the Col des Thures and the Col des Acles.
 The rectangular walled fort extends over an area of about 2.5 ha .
 The construction of Fort Chaberton on an even higher peak on the Italian side of the frontier rendered the Fort de l'Olive vulnerable to artillery from Chaberton, which was 900 m higher.
 The position was used by the French Army in the defense of Briançon until 1940, when it was part of the Fortified Sector of the Dauphiné.
 The fort took artillery fire from Chaberton during the Italian invasion of France in 1940.
Fort de Giromagny, also known as Fort Dorsner, was built near Belfort in northeastern France between 1875 and 1879.
 The fort forms the southern end of the defensive curtain of the Haute Moselle Region, abutting the Fortified region of Belfort, which lies to its south.
 The Haute Moselle defenses form a link between the fortified encampments of Épinal and Belfort.
 The fort overlooks the main roads to the northeast of Belfort, which form a crossroads at Giromagny.
The Swiss National Redoubt (German: "Schweizer Reduit" ; French: "Réduit suisse" ; Italian: "Ridotto nazionale" ; Romansh: "Reduit nazional" ) was a defensive plan developed by the Swiss government beginning in the 1880s to respond to foreign invasion.
 In the opening years of the Second World War the plan was expanded and refined to deal with a potential German invasion, that was planned, but never carried out.
 The term "National Redoubt" primarily refers to the fortifications begun in the 1880s that secured the mountainous central part of Switzerland, providing a defended refuge for a retreating Swiss Army.
The Fortified Sector of the Escaut ("Secteur Fortifié de l'Escaut"), also known as the Fortified Sector of the Schelde, was the French military organization that in 1940 controlled the section of the Maginot Line between the French border with Belgium and Valenciennes, a distance of about 30 km .
 Named for the Escaut River (more commonly known as the Schelde), the Maginot line in the Escaut sector consists of a single position, the "petit ouvrage" Eth, together with its supporting casemate Jeanlain, as well as an upgraded fort of the Séré de Rivières system, the Fort de Maulde.
 The remainder of the sector's fortifications consist of blockhouses and casemates arranged along a line of principal resistance about 2 km behind the frontier, with a second line on the edge of the Raismes Forest.
 The Escaut sector and the Fortified Sector of Maubeuge were the final sections of the Maginot line to be authorized, and were termed the "New Fronts."
 The Escaut sector was attacked during the Battle of France in late May 1940, resisting for a few days.
The Fort de Dailly is the largest component of Fortress Saint-Maurice, which is in turn one of the three principal fortified regions of the National Redoubt of Switzerland.
 Almost entirely subterranean, the Fort de Dailly was built in the Massif de Dailly to the east of Saint-Maurice beginning in 1892.
 With the Fort de Savatan, it comprises a fortress complex encased in rock high above the strategic Saint-Maurice valley, capable of commanding the valley from Chillon to Martigny.
 It is the central component of Fortress Saint-Maurice in terms of both its position and its military power.
 Construction began in 1892 and the fort became operational in 1894.
 The fort was nearly constantly upgraded with new artillery in increasingly secure positions.
 Following an incident in which three ammunition magazines exploded in close succession in 1946, the fort was repaired and upgraded with two fully automatic 150mm gun turrets with a range of 24 km .
 After reassessments by the Swiss Armed Forces of their requirements for fixed fortifications, Dailly was progressively closed down starting in 1995, with full closure at the end of 2003.
The Fort de Maulde, also known as Fort de Beurnonville and the Ensemble de Maulde, is located to the south of Maulde, France.
 It is part of the Fortified Sector of the Escaut, an extension of the Maginot Line.
 The Séré de Rivières system fort was built 1881-1884.
 In 1936-37 the old fort, commanding high ground behind Maulde, was altered for more modern fortifications.
 It was evacuated by its garrison in 1940 during the Battle of France as part of the French retreat from the border with Belgium.
The Fort de Cindey (Swiss designation A155) is a component of Fortress Saint-Maurice, which is in turn one of the three principal fortified regions of the National Redoubt of Switzerland.
 The Fort de Cindey was built in two steps: the first, between 1941 and 1946 and the second step, between 1948 and 1954 (the hospital, the artilleries casemates with the gunnery command and the ammunition magazines) .
 It was taken out of service in 1995.
 This fort was built in the Scex cliff face immediately to the west of Saint-Maurice to complement the existing Fort du Scex, built earlier in the same cliff.
 With the Fort du Scex, it comprises a fortress complex encased in rock high above the strategic Saint-Maurice valley.
 The fort was deactivated in 1995.
 It is now open for public tours during the summer months.
The Fort de St-Héribert or the Fort de Wépion is one of nine forts built as part of the Fortifications of Namur in the late 19th century in Belgium.
 It was built between 1888 and 1892 according to the plans of General Henri Alexis Brialmont.
 Contrasting with the French forts built in the same era by Raymond Adolphe Séré de Rivières, the fort was built exclusively of unreinforced concrete, a new material, rather than masonry.
 In 1914 the fort was heavily bombarded by German artillery in the Battle of Namur.
 Maizeret was upgraded in the 1930s to become part of the fortified position of Namur in an attempt to forestall or slow an attack from Germany.
 It saw action in 1940 during the Battle of Belgium, and was captured by German forces.
 The fort now belongs to the private Fondation Emile Legros.
 The foundation has already unearthed the main entrance and other areas.
Fort Knokke or Fort de Cnocke or Fort de la Knocque or Fort de Knocke was an important fortification that defended western Flanders from the 1580s until it was demolished in the 1780s.
 During its 200 year history, the place was held by the Spanish Empire, Kingdom of France, Habsburg Austria and the Dutch Republic.
 The existing defenses were improved in 1678 by the famous military engineer Sébastien Le Prestre de Vauban.
 The fort was attacked by the Grand Alliance in 1695 during the Nine Years' War but the French garrison successfully held out.
 It was captured from the French by a ruse in 1712 during the War of the Spanish Succession.
 Control of the fort and other strong places in the Austrian Netherlands was a key feature of the so-called Barrier Treaty in 1713.
 The French captured the fort after a two-month siege in 1744 during the War of the Austrian Succession.
 Emperor Joseph II had the citadel demolished in 1781.
 The site is on the Yser River about 8 km southwest of Diksmuide, Belgium.
The Fort du Scex is a component of Fortress Saint-Maurice, which is in turn one of the three principal fortified regions of the National Redoubt of Switzerland.
 The Fort du Scex was built in the Scex cliff face immediately to the west of Saint-Maurice beginning in 1911.
 With the later Fort de Cindey, it comprises a fortress complex encased in rock high above the strategic Saint-Maurice valley.
 The fort lost its combat function in 1984 and was entirely deactivated in 1995.
 It is now open for public tours during the summer months.

Question: Who developed this defensive plan in the 1880s that has Fort de Cindey as one of its three principal fortified regions?
Answer: the Swiss government