This book examines the Arch of Constantine through an integrated approach combining field archaeology, architectural history, and archaeometric analysis. Resulting from over a decade of research led by the Department of Antiquities Sciences at Sapienza University of Rome, the volume challenges earlier theories proposing an initial Hadrianic phase for the monument. Through stratigraphic excavations near the Meta Sudans, stone-by-stone cataloging of roughly 1,600 marble blocks, and geochemical testing on over 130 samples, the contributors demonstrate that the arch represents a unified Constantinian construction project. The work analyzes the systematic reuse of spolia—including architectural elements, victory reliefs, and statues from Trajanic, Hadrianic, and Antonine contexts—as a deliberate ideological and visual strategy designed to legitimize Constantine's authority within traditional imperial symbolism. Detailed technical evaluations further cover the monument's foundations, structural assembly, construction techniques, and post-antique history, offering a comprehensive reinterpretation of late antique Roman public architecture and urban planning.