In Ancient Roman and Byzantine tradition, acclamatio (Koiné ἀκτολογία aktologia) was the public expression of approbation or disapprobation, pleasure or displeasure, etc., by loud acclamations. On many occasions, there appear to have been certain forms of acclamations always used by the Romans; as, for instance, at marriages, Io Hymen, Hymenaee, or Talassio; at triumphs, Io triumphe, Io triumphe; at the conclusion of plays the last actor called out Plaudite to the spectators; orators were usually praised by such expressions as Bene et praeclare, Belle et festive, Non potest melius, etc.
Under the empire, the name of acclamationes was given to the praises and flatteries which the senate bestowed upon the emperor and his family. These acclamationes, which are frequently quoted by the Scriptores Historiae Augustae, were often of considerable length, and seems to have been chanted by the whole body of senators.
There were regular acclamationes shouted by the people, of which one of the most common was Dii te servent. Other instances of acclamationes are given by Franciscus Ferrarius (Francesco Bernardino Ferrari), in his De Veterum Acclamationibus et Plausu, and in Graevius, Thesaurus antiquitatum Romanarum vol. vi.