Israeli archaeologists have unearthed a wall beyond Jerusalem's old boundaries, showing the city built by biblical King David may have been much larger than previously thought, they said on Wednesday.

The Israel Antiquities Authority said it believed the 5-metre (16 ft) high wall was part of a two-storey structure demolished in 70 AD when the Romans sacked Jerusalem and destroyed the second Jewish temple built by King Herod.

"According to our findings, ancient Jerusalem ... was much larger than previously thought," Doron Ben-Ami of the authority told a news conference near the excavation site.

Ben-Ami believes the structure may have been a section of a palace belonging to Queen Helena of Mesopotamia, who converted to Judaism in the first century AD, and left behind her kingdom in modern-day Iraq to settle in Jerusalem.

The wall was found beneath a parking lot about 300 meters south of the area known as the Temple Mount to Jews and al-Haram al-Sharif to Muslims.

Ben-Ami said narrow openings discovered at the bottom of the wall may have been used by inhabitants to flee the building as the Romans smashed it to pieces during the sacking of Jerusalem.

"We know that the structure was not destroyed by fire but it was destroyed purposely by dismantling its walls, which were made of stones," Ben-Ami explained.

The excavations yielded artifacts dating back to the early Islamic, Byzantine, and Hellenistic eras, as well as the first and second Temple periods.

The Temple Mount was the site of the ancient second Jewish temple, the only remnant of which is the Western Wall, the holiest shrine for Jews.