In Rome during the period of the Persecution, paintings on the ceilings and walls of the catacombs (underground burial vaults and funeral chapels) illustrated important Christian narratives to teach and inspire the faithful.. Early Christian art marks a bridge between the old, pagan world and new Christian ideas. In this period of transition, artists used familiar Roman stylistic traits and Roman techniques to present the symbols and narratives of the Christian faith. In this period, symbolic visual language became increasingly significant. These images were intended to commemorate the dead and to inspire the faithful with messages of eternal life promised to the true believer.  Subjects reflecting belief in resurrection into a heavenly space presided over by a gentle shepherd Christ figure were frequently depicted. The language of symbols or iconography  became increasingly significant.  Sculpted forms on sarcophagi were the important type of three dimensional art during the Early Christian period in Rome and the old Roman themes (portraits, classical subjects, imperial propaganda) declined in importance as Christian subjects rose in importance.  This was especially true after the Recognition, after which the need to build large scale structures to house the faithful prompted innovation and experiment in architecture as the impulse to celebrate Christianity was the catalyst for a series of spectacular building programs in Rome and beyond in the larger Christian world. As in painting and sculpture, older, often pagan forms were the basis for these new buildings. The old classical plans and forms were modified and rethought to properly function in the new Christian world.