Fig. 1From: Biodeterioration of Roman hypogea: the case study of the Catacombs of SS. Marcellino and Pietro (Rome, Italy)Planimetry of the Catacombs of SS. Marcellino and Pietro showing the intricate system of galleries and chambers. Black and yellow lines represent upper and lower levels, respectively, whilst the red line shows the area open to the tourists (Courtesy of the Pontificia Commissione di Archeologia Sacra, Roma)Back to article page