"Massimo Osanna, director of the Pompeii Archaeological Park, and Luisa Ferro and Giulio Magli of the Polytechnic University of Milan, suggest that images in a floor mosaic in a Pompeian house may be related to the practice of surveying, according to information released by the Polytechnic University of Milan. Roman survey technicians, known as gromatici, employed a cross-shaped instrument called a groma. A cord hanging from each of the perpendicular arms of the cross ended with a weight or plumb bob that could be used to create plumb lines. Thus, the tool allowed surveyors to establish true vertical and horizontal lines when planning towns and aqueducts. One groma has been uncovered at Pompeii, but their use has only been known from texts dating to the medieval period. Osanna and his colleagues explained that one of the mosaic images in the House of Orion resembles those seen in a medieval text. It consists of a square inscribed in a circle, which is cut by two perpendicular lines. One of the lines aligns with the longitudinal axis of the structure’s atrium. A second image, made up of a circle inscribed with a cross, appears to depict a groma. The researchers think the owner of the home may have belonged to the surveyors' guild, or the structure may have been used for guild meetings. "