Archaeological workers in western Japan have unearthed a shield-shaped mirror and a long sword at an ancient burial mound.

The Tomio-Maruyama Tumulus in Nara City dates from the latter half of the fourth century. It is the largest circular burial mound in Japan.

The city's board of education began excavating the mound's burial site in October.

The bronze mirror and iron sword were found in clay that covered the coffin.

The mirror is more than 60 centimeters long and about 30 centimeters wide, and its top is rounded to resemble a shield. It is the first discovery of a shield-shaped mirror.

Its surface had been polished to reflect light, while the backside is decorated with images of gods and animals placed in a circle and patterns such as those resembling the teeth of a saw.

It also has a protrusion in the middle through which a string may have been threaded.

The sword, corrugated and more than 2.3 meters long, is the oldest of its type found in Japan and the longest of contemporary swords unearthed in East Asia.

Osaka University Professor Fukunaga Shinya says the mirror, in particular, is a masterpiece from this era, likely made by craftsmen with the highest skills.

Fukunaga believes the person interred at the Tomio-Maruyama Tumulus was a key figure who supported the Yamato Sovereignty.

However, because the mirror and sword were found at the foot of the mound, rather than from the burial site at the top of the mound, Fukunaga believes they were given to the key figure's close aide, who was buried with the artifacts at the lower site.