Final answer:
The correct answer is C) Triumphal Arch, which is a monumental structure that celebrates significant military victories and the emperors who won them, exemplified by the Arch of Septimius Severus and the Arch of Constantine in Rome.
Step-by-step explanation:
The answer to the question "A monumental memorial arch erected astride the line of march of a victorious army during its triumphal procession" is C) Triumphal Arch. These arches have been historically used to commemorate significant victories and the rulers who achieved them. For instance, the Arch of Septimius Severus and the Arch of Constantine are both prominent examples of triumphal arches in Rome, embodying both the commemoration of military successes and the celebration of imperial authority. The triumphal arch served as a visual representation of the continuity of the empire and its rulers, adorned with reliefs and inscriptions praising their achievements, as seen with other well-known examples like the Arch of Titus and Trajan's Column.