A new imperial era began with Emperor Naruhito's accession to the Chrysanthemum Throne on Wednesday, a day after the abdication of his father, former Emperor Akihito. The following are questions and answers related to the history of the Japanese imperial household.

Q: What is the role of the emperor?

A: The emperor was considered divine under the prewar Meiji Constitution. But the postwar Constitution defines him as "the symbol of the state and of the unity of the people" with no political power. Each emperor is expected to explore his own role in that capacity. Former Emperor Akihito, 85, frequently visited areas hit by natural disasters with former Empress Michiko, 84, to encourage victims. They also visited war memorials to mourn for the war dead and pray for peace.

Q: How far back does the Japanese imperial line go?

A: Emperor Naruhito, 59, is considered the 126th emperor in what is believed to be the world's oldest hereditary monarchy stretching back more than 2,600 years. The line includes early mythological leaders whose existence is disputed, including the first Emperor Jimmu, who is said to be a descendant of the Shinto sun goddess Amaterasu and have ascended to the throne in 660 B.C.

Q: Who is in line to the throne?

A: As the 1947 Imperial House Law stipulates that only males of the patrilineage can ascend the throne, there are currently three heirs among the 18 members of the imperial family -- the emperor's younger brother Crown Prince Fumihito, 53, his son Prince Hisahito, 12, and the emperor's uncle Prince Hitachi, 83. Concerns about the stability of succession exist as Prince Hisahito is the only male in his generation.

Q: Were there women rulers in the past?

A: Eight women ascended the throne in the past. All of them were members of the imperial patrilineage and were usually place fillers between male emperors. Debate about whether to allow female accession or emperors from matrilineal branches through amendment of the law has been raised to ensure stable imperial succession, but no substantial progress has been made.

Q: Is the latest imperial succession unique?

A: Former Emperor Akihito became the first monarch in almost 200 years to abdicate. He signaled his wish to do so in a rare video message in August 2016, citing concern that his advanced age may render him unable to fulfill official duties.

It was relatively common for emperors to abdicate in the past, but after the practice was banned in the Meiji Era (1868-1912), succession occurred only after emperors died. The last abdication was by Emperor Kokaku in 1817 and former Emperor Akihito became the 59th monarch to step down among 125 emperors in Japan. The abdication required one-off special legislation in 2017 to enable him to relinquish the throne.

Q: What will happen to former Emperor Akihito?

A: He will move out of the Imperial Palace together with former Empress Michiko and eventually reside at the Sento Imperial Palace in the Akasaka Estate, the current residence of Emperor Naruhito and his family, after renovation work. In the meantime, the retired couple will live in the Takanawa Imperial Residence. The former emperor, a keen marine biologist, is expected to continue his research on gobies, on which he has written 32 academic papers since 1963.

(The Imperial Palace (top) and the Togu Palace (bottom center) in Tokyo, March 2019)