Theprocessemployedincementingthematerialsofthevitrifiedfortswasthenperfectlyunique。Theprocessesemployedtoobtainthenecessaryheatvariedaccordingtocircumstancesandaccordingtothenatureofthematerialsused。AtSainte-SuzanneandatLaCourbemarinesaltwasusedasaflux。CaptainPrevot[244]thinksthatthewallsweresmearedwithacoatingofclay，andthatasinthebakingofbricksspaceswereleftbetweensoastoproducemoreintenseheat。M。deMontaiglonisofopinionthatthebuildingswereinthefirstinstanceerectedwithouttheuseofanycalcareousorargillaceousmaterial，andthatglassinastateoffusionwaspouredoverthemafterwards，thisglassconsolidatingthemandformingwiththemoneindestructiblemass。M。Thuotseemsmuchdisposedtosharethislastopinion，buthethinksthatsomechemicalmaterialssuchassodaorpotashwerealsoused。Yetoneotherpossiblesolutionmaybementioned，asolutionwhichisbecomingmoreandmoregenerallyaccepted，namelythatthegranitewasnotafterallreallymelted，butthatthevitrificationshouldeitherbeattributedtothefusionoftheargillaceousmass，whichhasbeensubjectedtoanigneoustransformation，suchasthatwhichoftentakesplaceinfurnacesforbakingbricksandinlime-kilns。[245]
Whateverexplanationwemayaccept，however，theprocessesemployedcertainlybearwitnesstoamuchmoreadvancedstateofcivilizationthanwasacquiredintheearliestagesofhumanity。Wehavebeenledbythegreatinterestandmysteryofthesubjecttodwelllongeronitthanweintended，andwemusthastentoreturntoprehistorictimeswithadeterminationnottotransgressagain。
Fortificationsareaproofofcombinedactionleadingtoacommonend；theyimplysocialorganization，chiefstocommand，workmentoobey。Arecentdiscoveryenablesustoformaveryaccuratepictureofprehistoricmengatheredtogethernotonlyforpurposesofdefence，butinasocietyalreadyrich，industrious，and，ifwemaysospeak，learningtocultivatetheartsofpeace。
TheAEgeanSeahaseverbeenthetheatreofigneousphenomena，andthethreelittleislandsofThera，Therasia，andAspronisi，whichshutintheBayofSantorin，arebuiltupchieflyofvolcanicmaterials。[246]In1573aneruptiveconesuddenlyappeared；in1707theinhabitantsofSantorinsawriseupashortdistancefromtheirshoresarockthatincreasedinsizeforseveraldaysandthensuddenlysplitup。Thissplittingupwassucceededbyagreateruptionofincandescentmaterials；aneruptionwhichlastedfornolessthanfiveyears，formingattheendofthattimeanislandsome400feethighby3，279feetincircumference。In1866，aftermanyviolentshocksofearthquake，thegroundwasrentasunderonthisislandandmassesofvolcanicmatterwerebelchedforth，whilstontheothersideoftheislandthesoilsanktosuchadegreethatcanoeswereusedtogettohouseswhichbutthedaybeforewereninefeetabovethesea-level。Thiseruptionwentonuntil1870，andthequantityofscoriaevomitedforthduringitscontinuanceweldedthreeislets，whichhadhithertobeenseparate，totheprincipalisland，ofwhichtheynowformpart。OnenteringtheBayofSantorinweseeoneverysidebanksoflava，bedsofscoriae，andpilesofcindersofapurplish-graycolorrisingincliffstoaheightofmorethan1，312
feet。Allthesematerialsaretheresultofinnumerableeruptions，andthecentralcraterofthevolcanoisprobablysituatedaboutthemiddleofthebay。Itissupposedthatatonetimeaconicalmountain，from1，958to2，600feethigh，rosewheresoundingsnowgiveadepthofwaterofover1，300feet。Asuddenbreakupofthemountainprobablyproducedthisabyss，andformidableeruptionshaveledtothepouringforthofimmensequantitiesofpumice-stone。Thethreeisletsmentionedabovewouldbetheremainsoftheoldcentralcone，andabedofpumice-stonefrom98to131feetthickisspreadoverthewholeoftheirsurface，tellingofaviolentcataclysmofwhichneitherhistorynortraditionhaspreservedthememory。