[85] But Sixtus V. (+ 1590) did not complete the lantern surmounting the dome, upon which the gilded cross was placed November 18, 1593. [86] Vincenzo Briccolani: _Descrizione della basilica vaticana_, third ed. Roma, 1816.--Pietro Ercole Visconti: _Metrologia vaticana_. Roma, 1828. [87] The baldacchino raised with questionable taste above the ciborium of Arnolfo di Cambio, a pupil of Nicolò Pisano (A. D. 1285), rests on four columns of Oriental alabaster, from the quarries of Sannhur, in the district of the Beni Souef, offered to Gregory XVI. by Mohammed Ali, viceroy of Egypt. The pedestals are inlaid with malachite, a present from the emperor Nicholas of Russia. [88] _Sulla grandezza e disposizione della primitiva basilica ostiense_. Roma, 1835. [89] _Acta apost. apocrif._ p. 1-39. Lipsiæ, 1851. [90] See: _Die Grabplatte des h. Paulus: neue Studien über die römischen Apostelgräber_, von H. Grisar, S. I. In the _Römische Quartalschrift_, 1892. Heft. I., II. [91] See chapter ii., p. 99. [92] My map of ancient Rome (scale 1:1000), which has cost me twenty-five years of labor, will be published in forty-six sheets measuring 0.90 m. × 0.60 m. each. The first, comprising sheets nos. iii., x., xvii., xxiii., xxx., and xxxvi. (from the gardens of Sallust to the Macellum Magnum on the Cælian), will be ready in May, 1893. The plan is drawn in five colors, referring respectively to the royal, republican, imperial, mediæval and modern epochs. [93] The basilica of S. Valentine, discovered in 1886, by our archæological commission, is mentioned on p. 120 of the present volume. CHAPTER IV. IMPERIAL TOMBS.[94] The death and burial of Augustus.--His will.--The Monumentum Ancyranum.--Description and history of his mausoleum.--Its connection with the Colonnas and Cola di Rienzo.--Other members of the imperial family who were buried in it.--The story of the flight and death of Nero.--His place of burial.--Ecloge, his nurse.--The tomb of the Flavian emperors, Templum Flaviæ Gentis.--Its situation and surroundings.--The death of Domitian.--The mausolea of the Christian emperors.--The tomb and sarcophagus of Helena, mother of Constantine.--Those of Constantia.--The two rotundas built near St. Peter's as imperial tombs.--Discoveries made in them in the fifteenth and sixteenth centuries.--The priceless relics of Maria, wife of Honorius.--Similar instances of treasure-trove in ancient and modern times.