Locals call it Oud Kasteel - the Old Castle - to tell it apart from its younger sibling a kilometer away. The donjon at its heart is the original, raised in local brown sandstone by the Lords of Wesemael in the late fourteenth century, walls more than two meters thick where the medieval mason thought a siege might come. It almost certainly replaced an earlier fortress that nobody bothered to write down. The House of Merode has lived here for more than five hundred years, layering each century onto the last. The sixteenth century softened the fortifications and added comfort. Romantic restorations in the 1800s put medieval flourishes back on. The interiors hold Córdoba leather wall hangings, family portraits, the heavy furniture of an aristocracy that survived everything Europe could throw at it. The Knights' Hall, the dining room, the drawing room - they open to visitors one weekend a year, the first weekend of July, for the Kasteelfeesten.

Across the Nete river from the castle stretches sixty hectares of formal French landscape, a rectangular pond drawing the eye toward a distant point of perspective. Fieldmarshall Jean-Philippe-Eugène de Mérode-Westerloo commissioned it at the start of the eighteenth century after returning from court. He had seen Louis XIV's gardens at Versailles and wanted the same geometry of power expressed in his own grounds. Closer to the castle, twelve hectares of English landscape park curl around the moats, the ponds connected to the castle's water like a single circulatory system. Two centuries, two philosophies of beauty, both still here. From the air the contrast is startling - the French side rigid as graph paper, the English side wandering like a thought.

Jeanne de Mérode was born in Paris in 1853, daughter of the Marquess of Westerlo and Princess Marie-Nicolette d'Arenberg. She never married. She devoted her inheritance to religion and to the people of Westerlo, financing a church, a school, a monastery in Heultje, a home for the elderly, and a carpet factory that gave the town's young women work. When her brother died in 1908 she planned to leave for her father's castle at Grimbergen. The town begged her to stay. She agreed - and commissioned an entire new castle to live in, just a kilometer from the old one. Pierre Langerock designed it in neo-Gothic to echo the abbey of Tongerlo, with four small towers, a large one, and a bell tower shaped like a crown. Inside, beneath the historical surfaces, it was startlingly modern for a Belgian country house in 1912: steel roof beams, electric elevator, central heating, running water, indoor bathrooms.

When German troops crossed the border in May 1940 they took the New Castle for a local Nazi headquarters. Jeanne moved back to the Old Castle and died there on 1 July 1944, two months before liberation, ninety-one years old and never again to see her own bed. She left her castle to a monastic order of sisters. The church used it as a home for retired priests until the 1970s, when the municipality of Westerlo bought it. It has been the town hall ever since. Couples marry there. Tax forms are processed in rooms that once held a countess's library. The chapel still stands. The altarpiece on which she prayed every day is in Manhattan.

Two more castles complete the count. The Castle de Meeûs d'Argenteuil, in nearby Tongerlo, was built during and after the First World War by the Baron de Trannoy. Another, built in the 1920s by the Naets family of notaries, sits quietly among them - the youngest of Westerlo's accumulation of stone manor houses. Approaching the town from the air, look for the moats first. They appear as dark, almost perfect rectangles in the green countryside, water older than any building it now reflects, fed by the Nete and the ponds and the small drainage channels that have outlasted every owner whose family name once appeared on the deeds.