The groma is an ancient surveying instrument used by the Romans for land measurement and construction. It consists of a horizontal cross made of wood or metal, mounted on a vertical staff. The cross has plumb lines hanging from its ends, allowing surveyors to establish right angles and straight lines accurately. Surveyors would use the groma to create straight boundaries and align structures, ensuring precision in their work. This tool was essential for the development of Roman infrastructure, including roads and buildings, and is considered a precursor to modern surveying equipment.