Constantine provided two measures on Sunday's observance. The first one was the institution of a weekly market (nundinae) every Sunday in the district of Aquae Iasae (Pannonia Superior), dated between the years 316 and 321. The second one is the enactment of a general law, directed to the vicar of the pretorian praefect in the City of Rome, Helpidius, that stablished the Sunday as dies festus, and, consequently, an official and private rest day, with some exceptions. The terms of the Constantinian dispositions on Sunday were not relative to Christianity. Namely, Constantine legislated on Sunday under the heathen denomination of Dies Solis ("the Day of the Sun"), and never as the Christian Dies Dominicus ("the Day of the Lord"). In fact, the Constantinian dispositions on Sunday indicated the Dies Solis as a day of weekly rest in order to furnish the Roman citizens a weekly space of time dedicated to the observance of vows to the Roman gods. According to the text of the laws, the first aim of the Constantinian dispositions was the emperor's achievement of heathen piety (pietas), following the Roman consuetudines. Taking into account that these dispositions were enacted during 323-324, the critical period previous to the second civil war between Constantine and Licinius, they could be considered as a form of Constantinian adhesion to Roman customary religious forms, in opposition with the syncretistical religious cults developed by his reival Licinius in the Eastern provinces of the Empire. Nevertheless, the Constantinian measures on Sunday were also meant to the Christian citizens, who recognized the Sunday as the "Holy Day of the Lord" after 324. Later, in 335-336, Eusebius of Caesarea developed this identification in De laudibus Constantini, with the emperor's approvement, but it was not until 386 that the Sunday received a legal sanction as the "Day of the Lord".