ello ▁De ▁Sp ina ▁and ▁Bon aggi unta ▁Ci ab atti , ▁whose ▁names ▁were ▁found ▁eng ra ved ▁on ▁a ▁stone . ▁The ▁l ighth ouse ▁was ▁built ▁on ▁an ▁emer ging ▁rock ▁surrounded ▁by ▁the ▁sea ▁at ▁the ▁south ▁entrance ▁of ▁the ▁har bor . ▁The ▁structure ▁of ▁the ▁l ighth ouse ▁is ▁formed ▁by ▁a ▁pol yg onal ▁bas ement ▁of ▁ 1 3 ▁sides . ▁Over ▁everything ▁is ▁a ▁tower ▁formed ▁by ▁two ▁cyl ind ers . ▁Each ▁cyl inder ▁has ▁an ▁emb att led ▁bal con y ▁and ▁a ▁lan tern ▁at ▁the ▁top . ▁The ▁structure ▁consists ▁of ▁ 1 1 ▁flo ors ▁connected ▁to ▁each ▁other ▁by ▁a ▁ ▁spir al ▁st air case . ▁Every ▁floor ▁is ▁ ▁high ▁with ▁the ▁exception ▁of ▁the ▁first ▁and ▁second ▁flo ors ▁which ▁are ▁respectively ▁ ▁and ▁. ▁The ▁lower ▁part ▁of ▁the ▁l ighth ouse ▁is ▁made ▁of ▁four ▁cyl ind ers ▁of ▁decre asing ▁diameter . ▁The ▁upper ▁part ▁of ▁the ▁l ighth ouse ▁is ▁made ▁of ▁three ▁cyl ind ers ▁which ▁results ▁in ▁the ▁tower ▁becoming ▁th inner ▁toward ▁the ▁sum mit . ▁ ▁The ▁l ighth ouse ▁was ▁originally ▁built ▁with ▁white ▁Ver ru ca ▁stone ▁from ▁San ▁Giul iano ▁cave ▁near ▁P isa . ▁O il ▁l amps ▁were ▁initially ▁used ▁for ▁the ▁light ▁and ▁were ▁then ▁replaced ▁by ▁com pressed ▁oil . ▁In ▁ 1 8 4 1 , ▁F res nel ▁l ens ▁were ▁installed ▁and ▁ac et yl ene ▁gas