The Roman antiquities, t. 3, Plate XVI. Plan and section of the Mausoleum of S. Emperor Constantine`s mother Helena ta, on the Via Labicana. 

This etching by Giovanni Battista Piranesi, a renowned 18th-century Italian artist, depicts the plan and section of the Mausoleum of Helena, the mother of Roman Emperor Constantine. Located on the Via Labicana, the mausoleum's architectural details are meticulously rendered, including the circular ground plan and the cross-shaped interior space. Piranesi's work, known for its precise detail and dramatic perspective, offers a glimpse into the grandeur of Roman architecture and the enduring legacy of its ancient structures.