Complex sentence: Supplicatio in ancient Rome was a solemn thanksgiving or supplication to the gods decreed by the senate: all the temples were opened, and the statues of the gods placed in public upon couches (pulvinaria) to which the people offered up their thanksgivings and prayers.
Split into simpler sentences: Supplicatio in ancient Rome was a solemn thanksgiving or supplication to the gods decreed by the senate. All the temples were opened, and the statues of the gods placed in public upon couches (pulvinaria) to which the people offered up their thanksgivings and prayers.