Look at a satellite photograph of the city of Sakai and you will see something odd. Among the grey grid of roofs lie dark green shapes, some shaped like keyholes, ringed by water, sitting between houses and rail lines as if the city were growing around them. These are the Mozu kofun, great burial mounds raised for the rulers of the Yamato kingdom in the fifth century, and they form the western half of the Mozu-Furuichi group that was inscribed as World Heritage in 2019. The largest, the Daisen Kofun, is traditionally attributed to Emperor Nintoku and is one of the biggest tombs in the world by area, about half a kilometre long.
Maruhoyama sits in that landscape, one of the smaller companions of the giants, and it is here that the scale of the group becomes clear. Kings were not buried alone. Around the great mounds lay satellite tombs for relatives, officials and perhaps favourites, and when you walk the paths between them you realise it was a whole political landscape in earth and water. Workers placed haniwa, hollow clay figures of houses, horses and people, on the mounds, and some of these are on display in the Sakai City Museum.
Riding in is straightforward but needs patience. Sakai is a port city of nearly eight hundred thousand people on Osaka Bay, with heavy industry and busy roads, and the old moat paths and parks sit between the main thoroughfares. Use side streets for the final stretch, keep to the low limits, and park in a designated space, because bikes left on pavements in Japanese cities attract quick attention. Fuel is plentiful in the surrounding suburbs, and Matsubara, a few kilometres east, has more than a hundred thousand people. Sakai was once a rich merchant town, famous for its knives, which are still made here, and for the tea master Sen no Rikyu, who was born here in the sixteenth century.
Autumn mornings are cool and clear, with mist sometimes on the moats, and spring brings cherry blossom. Summers are brutally humid, and typhoon rain can come in September. The Kongo and Katsuragi hills, a short ride south-east, give you the twisting mountain roads this plain lacks, so consider the kofun a calm first stop, with the real riding afterwards.