Iwakuni-shi

In the 2020 Population Census, this city’s population was 129,125 — about 129,000. To note first here: the surge of more than forty thousand, from 103,507 in 2005 to 143,857 in 2010, is not the result of people increasing naturally. It owes to the 2006 merger of the former Iwakuni City with six surrounding towns and one village, and the step in the numbers mirrors that merger. A broad expanse of the prefecture’s east was bound into one city, and both the city area and the population widened at once.

On top of that, looking inside after the merger, from 143,857 in 2010 to 129,125 in 2020 it fell by nearly fifteen thousand over ten years. Those under 15 also fell by more than four thousand, from 18,596 in 2010 to 14,495 in 2020. The share aged 65 and over rose from 20.2% in 2000 to 35.7% in 2020, passing thirty-five percent. The household-with-children share is 17.4% (2020), the Childcare Waitlist has been zero in recent years, and the Fiscal Capacity Index was 0.54 in fiscal 2023. The figure of a castle town widened by merger, growing old fast while losing population, appears in the numbers. Why it takes this shape cannot be read without going back over the history of a castle and a bridge.

Iwakuni’s skeleton consists of a single river, the Nishiki, and the castle and castle town facing each other across it. In 1608, Kikkawa Hiroie, who became the first lord of Iwakuni, built Iwakuni Castle on a mountaintop, making the Nishiki River its natural outer moat. But this castle, by the policy of the Edo shogunate allowing only one castle per province (the One-Castle-per-Province Edict), was torn down a mere seven years after its building. The castle was lost early, but on Yokoyama on the opposite bank of the river spread a castle town where the residences of the Kikkawa house and its chief retainers stood in rows.

What tied together the town that had lost its castle was a single bridge raised over the river. In 1673, Kikkawa Hiroyoshi, the third lord, raised a bridge linking five wooden arches over the Nishiki River. But this bridge was swept away by a flood the year after it was raised, and, with improvements added, was raised again. The rebuilt bridge thereafter kept its grand figure unswept away for about two hundred and seventy-six years. To raise an unsweepable bridge over a swift-flowing river — that ingenuity became the lifeline linking the castle town and the opposite bank.

And from the modern era on, on the delta spreading at the mouth of the Nishiki River, an airfield was placed — built in 1938, originally as a naval air corps, with the land carried over after the war to the present. What decided the city’s present shape was the Heisei merger. In 2006, the former Iwakuni City merged with six surrounding towns and one village, widening into a city area holding a broad expanse of the prefecture’s east. Beginning with Kikkawa Hiroie’s castle, linking castle town and opposite bank with the Kintaikyo, and widened by merger — Iwakuni’s present continues from this history of castle and bridge.

What characterizes Iwakuni is that, after the city area widened by merger, the fall of population and aging advance fast. In the ten years after the merger the total population fell by nearly fifteen thousand, and the aging rate passed thirty-five percent. This can be read as an expression of the city area bound by merger including many depopulating, aging former towns and villages of the hill-and-mountain interior. By making a broad expanse one city, the whole city’s numbers weave in not only the built-up area but the shrinking of the periphery.

The living-infrastructure numbers, too, mirror this shrinking. Elementary schools doubled at once from twenty-three to forty-nine by the 2006 merger, the school networks of the joined towns and villages bound just so. Thereafter consolidation advanced in stages in step with the fall of children, and in recent years it has fallen to around thirty-nine. Schools that increased all at once decrease together with the fall of children. The Childcare Waitlist has moved at zero in recent years. The town opened as Kikkawa Hiroie’s castle town and known for the Kintaikyo is, after holding a broad city area by merger, in a fast shrinking. The three movements — total population falling, children falling, aging passing thirty-five percent — are all the result of the built-up area and the hill-and-mountain interior bound by merger melting into one number. So long as one views the whole city’s value in a single line, the look of the built-up area and the shrinking of the periphery are both rounded into the same average.

Iwakuni’s functions are split across both banks of a single river, the Nishiki. Iwakuni Castle, which made the Nishiki River its natural outer moat, was itself torn down early, but its memory is carried over in the rebuilt keep. The Kintaikyo, raised to link the castle town and the opposite bank, is the crystallization of the ingenuity of raising an unsweepable bridge over a swift-flowing river. And the airfield spreading on the delta at the mouth of the Nishiki River has used the river-mouth landform in another form, as land use from the modern era on.

Iwakuni is a castle town where castle and bridge face each other across the river. From Kikkawa Hiroie’s mountain castle, to the Kintaikyo linking castle town and opposite bank, and then to a city of the prefecture’s east widened by merger — the geography of "making the Nishiki River a natural moat and raising over that river an unsweepable bridge" called the castle town and the bridge and shaped the town’s outline. To raise, over a swift-flowing river, an unsweepable bridge. That single ingenuity kept linking castle town and opposite bank even after the castle was lost. Iwakuni’s present has its backbone on the side of the bridge that, even after losing the castle, kept tying both banks — not on the side of the castle.