This brief notice of early Christian sculpture would be incomplete without some reference to the statue of the celebrated Hippolytus, bishop of Portus, the most remarkable known specimen of that class. It was discovered by some workmen digging near the church of _San Lorenzo fuori le mura_ in the year 1551, and probably originally stood in the adjacent Catacomb of Hippolytus. The martyr bishop is 393 represented as seated in a sort of episcopal chair. The figure is modelled with a classic grace and dignity superior to any examples of the Constantinian period. Indeed, the distinguished art critic, Winckelmann, declares it to be the finest specimen of early Christian sculpture extant. It was considerably mutilated, but has been skilfully restored, and now stands in the Lateran Museum. On the base of the chair is engraved a list of the published writings of Hippolytus,[664] and also the table which he constructed for determining the true period of the Easter festival. The discovery of an error in this table deprived it of much of its value; and the date of this monument is probably prior to that discovery, or the early part of the third century. Passing allusion should also be here made to the early Christian diptychs, specimens of which are found in almost every antiquarian museum. These were formed after the model of the imperial and consular diptychs, or registers of the public officers of Rome. They consisted of tablets of ivory, wood, or metal, folded together,[665] and bore 394 the names of the bishops, officers, or distinguished patrons of the church, and memorials of the martyrs and holy dead. These memorials were frequently read in the religious assemblies of the primitive church, especially on the anniversaries of the martyrs’ death. This practice led in course of time to the invocation of their aid in the Litany of the Saints, and to other errors of Romanism. The diptychs had also frequently elaborate bas reliefs of scenes from the biblical cycle, and in the age of image-worship bore the figures of the saints to whom a corrupt Christianity had begun to pay an idolatrous veneration. They became thus the prototype of the illuminated missal of the Middle Ages. [614] _Vetri ornati di figure in oro trovati nei cimiteri dei Cristiani primitivi di Roma raccolti e spiegati da Raffaele Garrucci._--Roma, 1858. [615] _Osservazioni sopra alcuni frammenti di vasi antichi di vetro ornati di figure trovati nei cimiteri di Roma._--Firenze, 1716. [616] Transtyberinus ambulator, Qui pallentia sulphurata fractis Permutat vitreis.--_Epig._, i, 42. [617] Sicche volendo i fedeli adornar con simboli devoti i loro vasi, erano forzati per lo più a valersi di artefici inesperti, e che professavano altre mestieri.--_De’ Vetri Cemeteriali._ [618] _Rom. Sott._, p. 283. [619] _Ibid._