Historical clues

A lack of surviving first-hand documentation on construction of the Forbidden City makes studies of its infancy difficult.

Yang Xincheng, a researcher of ancient architecture at the Palace Museum, said: "There should be blueprints and detailed construction maps when this site was first built. Unfortunately, most of them have been lost to history. From the remnants of documents, we can only gain scattered and vague descriptions of these early-stage palaces.

"We only know their approximate locations in the Forbidden City, but their exact position usually remains a mystery. Sometimes, even the names of some constructions are obscure for today's researchers," he said.

According to Yang, the layout for buildings within the present-day Forbidden City was basically formed during the reign of Emperor Jiajing (1522-66), who remodeled his home on a large scale, along with many other royal facilities to demonstrate his ambition.

"This left an unclear picture of the Forbidden City before his reign, which can only be redrawn through archaeology," Yang said.

In early Ming rhyming prose eulogizing the imperial city, two palaces-Dashan ("grand benevolence") and Renshou ("mercy and longevity")-are said to have probably existed in the area where the new heritage site was unearthed.

Ming Shilu also stated that Emperor Jiajing once ordered his Cabinet to discuss a proposal to demolish a Buddhist temple at the site and build a new residence for the empress dowager.

However, Xu and Wu think it is too early to connect their discoveries with historical records until more solid evidence emerges.

In 2014, other ancient constructions were unearthed under a square near Cining Gong (the Palace of Compassion and Tranquility), less than 100 m from the current archaeological work site. That area was also thoroughly reconstructed during Emperor Jiajing's reign, according to historical documents.