Question: Immerhof protected blockhouses that were constructed during a war that lasted how long?
Context: The Krepost Sveaborg was an Imperial Russian system of land and coastal fortifications constructed around Helsinki during the First World War.  The purpose of the fortress was to provide a secure naval base for the Russian Baltic fleet and to protect Helsinki and block routes to Saint Petersburg from a possible German invasion.  Krepost Sveaborg was part of Peter the Great's Naval Fortress, a coastal fortification system protecting access to Saint Petersburg by sea.  The central part of Krepost Sveaborg was the old fortress of Suomenlinna where the fortress headquarters were located.  Due to technological advances in artillery the old fortress was no longer capable of providing a sufficient protection, and a new main defensive line was built well beyond the old fortress boundaries.  New coastal artillery guns built on outlying islands protected Krepost Sveaborg from the sea, while fortified lines constructed around Helsinki were intended to stop any attacks on land.  The primary coastal guns were 10 in model 1891 guns and 6 in model 1892 Canet guns. Older 11 in model 1877 guns were also used.  In summer 1917 the fortress had two hundred coastal or anti-landing guns, of which 24 were 10-inch guns in six batteries, 16 were 6-inch Canet guns in four batteries and twelve were 11-inch guns in three batteries.  The artillery used in land fortifications included older coastal guns, old fixed carriage guns and newer light field guns.  In March 1917, Krepost Sveaborg had a total of 463 guns, although many of them were obsolescent.  Krepost Sveaborg was still partly incomplete in 1917 when the February Revolution halted most of the construction work.  Some further construction work was carried out during the remaining year, but all work halted during the October Revolution.  Following the Finnish Declaration of Independence, parts of the land fortifications were used in the Finnish Civil War.  The coastal fortifications were later taken over by Finland to protect Helsinki, while the land fortifications were mostly abandoned and disarmed. Ouvrage Immerhof, also known as Ouvrage Ferme-Immerhof, is one of the largest "petit ouvrages" of the Maginot Line of northeast France.  Located near the community of Hettange-Grande, it is 7 km north of Thionville between the "gros ouvrages" of Molvange and Soetrich, the closest "ouvrage" to the Luxembourg frontier.  It was part of the Fortified Sector of Thionville, in the Fortified Region of Metz, the strongest portion of the Line.  Apart from its function as a communication post between the neighbouring "gros ouvrages", Immerhof also controlled the road and railway routes from Luxembourg, which pass in the immediate vicinity.  In addition, Immerhof protected other Maginot works in the vicinity: the casemates of Kanfen, the infantry shelter of Stressling, the observation point and shelter of Hettange-Grande, and a number of nearby blockhouses constructed during the Phoney War. The Bridestones is a chambered cairn, near Congleton, Cheshire, England, that was constructed in the Neolithic period about 3500–2400 BC.  It was described in 1764 as being 120 yd long and 12 yd wide, containing three separate compartments, of which only one remains today.  The remaining compartment is 6 m long by 2.7 m wide, and consists of vertical stone slabs, divided by a now-broken cross slab.  The cairn originally had a stone circle surrounding it, with four portal stones; two of these portal stones still remain.  The site is protected as a scheduled ancient monument. The Battle of El Caney was fought on 1 July 1898, during the Spanish–American War in southeastern Cuba.  Lawton succeeded in capturing the town, fort and blockhouses and protected the right flank of the main American attack on the Heights of San Juan to the south. Wind Springs Ranch is a historic ranch complex located in the Wind Springs Creek Valley in Sioux County, Nebraska.  The present ranch, which was built around 1910, was the third European settlement constructed on the property.  The ranch has mainly raised cattle and sheep.  Settlers constructed two homesteads on the property in the 19th century, neither of which lasted long; the two homesteads only survive as archaeological remains.  In addition, the Fort Laramie to Spotted Tail Agency Road ran across the property in the 1800s, and Wind Springs was likely a campsite along the road; wagon ruts still remain along the road's path through the ranch.  Researchers have determined the existence of eighteen sites related to European settlement on the ranch; aside from the ranch itself, all are archaeological sites. Fort Defiance was one of the last garrisoned stockade forts constructed in territorial Wisconsin.  It was located approximately five miles southeast of Mineral Point, Wisconsin.  It was located in the booming lead mining region in an area of early settlement.  The fort was built by local settlers in 1832 when developing tensions over Native American land rights erupted into the Black Hawk War.  Although Fort Defiance did not experience attack, it did have a garrison of about 40 militia men who were said to be among the best drilled in the territory.  Fort Defiance had two blockhouses located at opposite corners of the stockade.  Within the walls were two buildings used to accommodate the garrison and the families of settlers in case of a siege.  There are no visible remains. La Reforma (English: The Reform ) or the Liberal Reform was initiated in Mexico following the ousting of centralist president Antonio López de Santa Anna by a group of liberals under the 1854 Plan de Ayutla.  From the liberals' narrow objective to remove a dictator and take power, they expanded their aims to a comprehensive program to remake Mexico governed by liberal principles as embodied by a series of Reform laws and then the Constitution of 1857.  The major goals of this movement were to undermine the power of the Catholic Church in Mexico, separate church and state, reduce the power of the Mexican military, and integrate Mexico's large indigenous population as citizens of Mexico and not a protected class.  Liberals envisioned secular education as a means to create a Mexican citizenry.  The liberals' strategy was to sharply limit the traditional institutional privileges ("fueros") of the Catholic Church and the army.  The law prohibiting the ownership of land by corporations targeted the holdings of the Catholic Church and indigenous communities - confiscating Church land.  Indigenous community lands were held by the community as a whole, not as individual parcels.  Liberals sought to create a class of yeoman farmers that held land individually.  No class of individualistic peasants developed with the Liberal program emerged, but many merchants acquired land (and tenant farmers).  Many existing landowners expanded their holdings at the expense of peasants, and some upwardly mobile ranch owners, often mestizos, acquired land previously held by communities.  Upon the promulgation of the liberal Constitution of 1857, conservatives refused to swear allegiance to it and, instead, formed a conservative government.  The result was a civil war known as the Reform War or Three Years' War, waged between conservatives and liberals for three years, ending with the defeat of the conservatives on the battlefield.  Victorious liberal president Benito Juárez could not implement the envisioned reforms due to a new political threat.  Conservatives had sought another route to regaining power, resulting in their active collaboration with Napoleon III's plans to turn the Mexican Empire into a part into the main American ally of the French empire.  Mexican conservatives offered the crown of Mexico to Hapsburg archduke Maximilian.  The French invasion and republican resistance to the French Intervention in Mexico lasted from 1862-67.  With the defeat of the conservatives and the execution of Maximilian, Juárez again took up his duties as president.  In this period from 1867 to 1876, often called the "Restored Republic" liberals had no credible opposition to their implementation of the laws of the Reform embodied in the 1857 Constitution. Hull Castle was an artillery fort in Kingston upon Hull in England.  Together with two supporting blockhouses, it defended the eastern side of the River Hull, and was constructed by King Henry VIII to protect against attack from France as part of his Device programme in 1542.  The castle had two large, curved bastions and a rectangular keep at its centre; the blockhouses to the north and south had three curved bastions supporting guns, and a curtain wall and moat linked the blockhouses and castle.  The construction project used material from recently dissolved monasteries, and cost £21,056.  The town took over responsibility for these defences in 1553, leading to a long running dispute with the Crown as to whether the civic authorities were fulfilling their responsibilities to maintain them. The Cape May Canal is a 2.9-nautical mile (3.3 mi; 5.4 km) waterway connecting Cape May Harbor to the Delaware Bay, at the southern tip of Cape May County, New Jersey.  There is a long history of unfulfilled plans for a canal across Cape May.  The canal was finally constructed by the United States Army Corps of Engineers during World War II to provide a protected route to avoid German U-boats operating off Cape May Point and to become part of the Intracoastal Waterway.  The canal was dredged as a wartime emergency measure in 1942 and was the final link in a protected waterway intended to allow coastal shipping to travel along the coast with a greatly reduced risk of attack from German submarines. The Phoney War (French: "Drôle de guerre" ; German: "Sitzkrieg" ) was an eight-month period at the start of World War II, during which there were no major military land operations on the Western Front.  It began with the German invasion of Poland on 1 September 1939 and the declaration of war by the United Kingdom and France against Nazi Germany on none }} , and ended with the German attack on France and the Low Countries on 10 May 1940.
Answer: eight-month period