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•EiffelTowerThetowerofhuqiuThetowerofpisaThetowerofpisaTheLeaningTowerofPisa(Italian:TorrependentediPisa)orsimplyTheTowerofPisa(LaTorrediPisa)isthecampanile,orfreestandingbelltower,ofthecathedraloftheItaliancityofPisa.ItissituatedbehindtheCathedralanditisthethirdstructureinPisa'sCampodeiMiracoli(fieldofMiracles).TheTowerofPisawasaworkofart,performedinthreestagesoveraperiodofabout174years.Thisfirstfloorissurroundedbypillarswithclassicalcapitals,leaningagainstblindarches.thetowerbeganleaningtothesoutheastsoonaftertheonsetofconstructionin1173duetoapoorlylaidfoundationandloosesubstratethathasallowedthefoundationtoshiftdirection..Thetowerbegantosinkafterconstructionprogressedtothethirdfloorin1178.Thiswasduetoamerethree-meterfoundation,setinweak,unstablesubsoil.Whatcausethetowerbecomealeaningtower?Theheightofthetoweris55.86m(183.27ft)fromthegroundonthelowestsideand56.70m(186.02ft)onthehighestside.Thewidthofthewallsatthebaseis4.09m(13.42ft)andatthetop2.48m(8.14ft).Itsweightisestimatedat14,500tonnes.Thetowerhas294steps.Thetowerleansatanangleof5.5degrees[1].Thismeansthatthetopofthetoweris4.5metersfromwhereitwouldstandifthetowerwasperfectlyvertical.TheconstructureofthetowerofpisaGalileoGalileiissaidtohavedroppedtwocannonballsofdifferentmassesfromthetowertodemonstratethattheirdescendingspeedwasindependentoftheirmass.Thisisconsideredanapocryphaltale,andtheonlysourceforitcomesfromGalileo'ssecretary.BenitoMussoliniorderedthatthetowerbereturnedtoaverticalposition,soconcretewaspouredintoitsfoundation.However,theresultwasthatthetoweractuallysankfurtherintothesoil.ThehistoryofthetowerDuringWorldWarII,theAlliesdiscoveredthattheNaziswereusingitasanobservationpost.AhumbleU.S.Armysergeantwasbrieflyentrustedwiththefateofthetower.Hisdecisionnottocallinanartillerystrikesavedtheedifice.OnFebruary27,1964,thegovernmentofItalyrequestedaidinpreventingthetowerfromtoppling.Amultinationaltaskforceofengineers,mathematiciansandhistorianswasassignedandmetontheAzoresislandstodiscussstabilizationmethods.Afterovertwodecadesofworkonthesubject,thetowerwasclosedtothepublicinJanuary1990Thefinalsolutiontopreventthecollapseofthetowerwastoslightlystraightenthetowertoasaferangle,byremoving38m3ofsoilfromunderneaththeraisedend.Throughthis,thetowerwasstraightenedby18inches(45centimeters),returningtotheexactpositionthatitwasin1838.Thetowerhasbeendeclaredstableforatleastanother300years.In1987,thetowerwasdeclaredaspartoftheCampodeiMiracoliUNESCOWorldHeritageSitealongwithneighbouringcathedral,baptisteryandcemetery.Afteradecadeofcorrectivereconstructionandstabilizationefforts,thetowerwasreopenedtothepubliconDecember15,2001.Itwasfoundthattheleanwasincreasingduetothestoneworkexpandingandcontractingeachdayduetotheheatofsunlight.SeeyouNexttime