Experts have discovered a third structure within the Kukulkan pyramid in eastern Mexico, revealing that it was built like a “Russian nesting doll”, experts said on Wednesday.

A 10m tall pyramid was found within another 20m structure, which itself is enveloped by the 30m exterior visible at the Mayan archeological complex known as Chichen Itza in Yucatan state.

The smallest pyramid was built between the years 550 and 800, engineers and anthropologists said.

The middle structure had already been discovered in the 1930s and dates back to the years 800-1,000 while the largest one was finished between 1050-1300.

The discovery suggests that the pyramid, also known as El Castillo (The Castle), was built in three phases.

“It’s like a Russian nesting doll. Under the large one we get another and another,” said Rene Chavez Seguro, project chief and geophysics expert.

Structures were built on top of each other for various reasons, including deterioration or the arrival of new leadership, said Denisse Argote, expert at the National Anthropology and History Institute.

The smallest pyramid was spotted using non-invasive scanning techniques.

The discovery could shed light on the original Mayan culture before it was influenced by populations from central Mexico, Argote said.

In 2015 archeologists discovered the Kukulkan pyramid was built atop a cenote, or underground river, which are common in the region and sacred to the Maya.

(The Guardian)