[RonBee]

Re:

After walking around the ancienty city, the archaeologists spotted a temple dating from the fifteenth century B.C. and then decided to explore the temple.
As the explore progressing, archarologists found a sacred room of this temple, on entering the sacred room, the archaeologists saw some fragments of some statues on the ground, after this, workman began digging and soon discovered a body of one statue.

Try:

After walking around the ancient city, the archaeologists spotted a temple dating from the fifteenth century B.C. and then decided to explore the temple. As the exploration progressed the archaeologists found a sacred room of this temple. Upon entering the sacred room, the archaeologists saw some fragments of some statues on the ground. Soon after that, the workmen began digging, and they soon discovered the body of a statue.

You can't separate "on" from the rest of the phrase.

on (upon) entering the sacred room = when they entered the sacred room