This paper describes 3D acquisition and modeling of the "Plastico di Roma antica", a large plaster-of-Paris model of imperial Rome (16x17 meters) created in the last century. Its overall size demands an acquisition approach typical of large structures, but it is also characterized by extremely tiny details, typical of small objects: houses are a few centimeters high; their doors, windows, etc. are smaller than 1 cm. The approach followed to resolve this "contradiction" is described. The result is a huge but precise 3D model created by using a special metrology Laser Radar. We give an account of the procedures of reorienting the large point clouds obtained after each acquisition step (50-60 million points) into a single reference system by means of measuring fixed redundant reference points. Finally we show how the data set can be properly divided into 2x2 meters sub-areas for allowing data merging and mesh editing..