Belgium is famously a country of three regions, and the Sonian Forest is the rare place that sits in all of them at once. It belongs to Flemish municipalities — Sint-Genesius-Rode, Hoeilaart, Overijse, Tervuren — and to the Brussels-Capital municipalities of Uccle, Watermael-Boitsfort, Auderghem, and Woluwe-Saint-Pierre, and to the Walloon towns of La Hulpe and Waterloo. The bookkeeping reflects the geography: Flanders manages 56 percent, Brussels 38, Wallonia six. There are private tracts as well, and the Kapucijnenbos — the Capuchin Wood — belongs to the Royal Trust. The forest pre-dates the political lines drawn through it. The 9th-century *vita* of Saint Foillan already calls the wood next to the abbey of Saint Gertrude the *Sonesian*. In the Middle Ages it pressed against the walls of Brussels itself, dense enough that Lord Byron borrowed the name Ardennes for it in *Childe Harold's Pilgrimage*.

At the start of the 19th century, the forest still covered about 25,000 acres. By 1830 it had been reduced to roughly 11,200. Napoleon contributed to that loss in spectacular fashion when he ordered 22,000 oaks felled to build the Boulogne flotilla, the invasion fleet he intended to throw at England. The fleet never crossed. The oaks did not come back. King William I of the Netherlands kept harvesting, and in 1815 a substantial slice of the wood near Waterloo was granted to the Duke of Wellington, whose Dutch title was Prince of Waterloo. That portion was eventually converted to farmland under the second duke. The Bois de la Cambre, the urban park that reaches up into Brussels itself, was carved out of the forest in 1861. Today the Sonian holds at about 4,421 hectares. Several trees are more than 200 years old, planted in the Austrian period when the empire ruled the southern Netherlands; their dense, even crowns are one of the things that makes the place feel like a cathedral with a green roof.

The fauna has thinned over the centuries. The forest once held 46 mammal species; seven have disappeared — the brown bear since about 1000, the wolf since around 1810, the hazel dormouse since 1842, the red deer, the badger, the hare, and the wild boar, which was thought extinct after 1957. Stag beetles have vanished too. Wild boar may be making a partial comeback: in 2007 fresh boar appeared in the wood; the Flemish nature agency suspects two to four animals released or escaped from captivity rather than a natural return. What has held on is the bats. The Sonian is a Natura 2000 site largely because of them: the greater mouse-eared bat, Geoffroy's bat, the barbastelle, the pond bat, and Bechstein's bat all live in the wood. Black woodpeckers and great crested newts share the protections. To reconnect populations cut apart by the highways slicing through the forest, an ecoduct — a 60-metre vegetated bridge — was built across the Brussels Ring R0 motorway, opened in June 2018, designed specifically for roe deer and boar to walk over the cars without being seen by them.

The forest has always attracted people who wanted to think clearly. John of Ruysbroeck, the great Flemish mystic, founded his monastery at Vauvert near Groenendaal here in the 14th century. Cistercian, Benedictine, and Dominican women's communities all settled in the wood over the medieval centuries. Habsburg emperors hunted these glades; the *Hunts of Maximilian* tapestries in the Louvre depict the chase through these trees. Auguste Rodin painted the forest while living in Brussels in the 1870s. The most recent memorial belongs to a quieter grief. On the Drève de l'Infante, in the middle of the wood, the landscape architect Bas Smets designed *Memorial 22/03* for the victims of the 2016 Brussels bombings at Maelbeek metro station and Brussels Airport: 32 birch trees, one for each person killed, planted inside a circular canal that sets them apart from the rest of the forest. Smets called it a place of silence and meditation. He chose birch because it grows fast, lives for less than a century, and reminds us, plainly, that grief is a thing trees can hold.