The church's base measures 51-by-30 yards, and archaeologists estimate its columns stood 20 feet tall and its wooden ceiling would have been about 50 feet high, al-Assaad said.
A small amphitheater also was found in the church's courtyard where experts believe Christian rituals were practiced, al-Assaad said.
"In the northern and southern parts of the church there are two rooms that are believed to have been used for baptisms, religious ceremonies, prayers and other rituals," he said.
Ancient Palmyra, located some 150 miles northeast of Damascus, was the center of an Arab servant state to the Roman empire and thrived on caravan trades across the desert to Mesopotamia and Persia.
Under the third-century Syrian Queen Zenobia, the city rebelled against Roman rule and briefly carved out an independent desert Arab kingdom before being reconquered and razed by the Romans.