As the waterway arrives at the coast, it widens into a spectacular bay; unique, unspoilt wetlands whose form and colours change with the tide. The wetlands are inundated by the sea at high tide, drained at low tide, when they are transformed into undulating grassy dunes, channels and eddies.

When the tide is out, the bay, seen from inland, seems to have no clear point of focus, with a seemingly endless horizon.

On closer inspection, though, it becomes clear the flats are alive with movement: duck hunters trekking out to hides; fishermen digging in the sand for clams; seals flopping on sun-warmed sand banks; horses galloping along the water’s edge; sheep grazing on the exposed salty grass.

And above it all, thousands of birds flitting back and forth, because this is one of the major migratory crossroads of Europe.

This bay, which stretches between the picturesque resorts of Saint-Valéry-sur-Somme and Le Crotoy, is where William the Conqueror assembled his fleet before sailing to England for the Battle of Hastings, in 1066.

Inland, where the Abbeville road splits towards, to the south, Saint-Valéry, and the north, Le Crotoy, is Noyelles-sur-Mer. This bucolic backwater has a tiny railway station, with the occasional train still stopping off en route between Paris and Calais.

Opposite the station is the red-brick Relais de la Baie, a cosy bistro, antique store and bed-and-breakfast run by France and Philippe David.

The friendly pair are used to pointing tourists in the direction of one of the Somme’s most unexpected war sites, situated at the end of a narrow, dusty mile-long track: Le Cimetière Chinois.

Surrounded by meadows, golden wheat fields, and grazing cows and horses stands a ceremonial arch etched with Chinese characters. Beyond, lines of simple white stones mark the graves of 841 men, all of them from China.

Each bears a Chinese Labour Corps (CLC) number, some actual names, with English inscriptions such as, “A good reputation endures for ever”, “Faithful unto death” and “A noble duty bravely done”.

According to records, some 140,000 contracted labourers were shipped from rural Shandong province by the British to provide manpower for the war effort in France. More than 80,000 of these CLC members were stationed in Noyelles.

Contracted for five years, each was paid one franc a day, with just a single day off annually, to celebrate Lunar New Year. The fortunate ones repaired roads or transported goods, worked in mines or on farms; others dug trenches on the battlefields and removed the dead.

When their contracts ended, in 1920, most returned home. But around 3,000 settled in France, in the process forming Paris’ first Chinatown, by the Gare de Lyon station, where many found work repairing the railway.

The capital’s Chinatown has long since moved on to the Belleville and Choisy neighbourhoods, though there remains a plaque and a life-size statue of a Shandong labourer outside the Gare de Lyon.

In Noyelles, impassioned residents have been documenting the history of the cemetery for more than 40 years – since mayor Claude de Valicourt founded the Au Fil du Temps Association – and from 2018, representatives from China’s Paris embassy have attended the annual Qing Ming commemoration, along with members of the Anciens Legionnaires d’Origins Chinoise, proudly dressed in their French Foreign Legion uniforms and adorned with medals, and other Chinese associations across France.

The current Au Fil du Temps president, Michel Galliani, possesses a trove of historical pictures documenting life in the Chinese camp, which included a hospital and even a pagoda as well as their prison-like barracks.

This material can easily be seen online and the association welcomes prearranged group visits; among those who have visited were pupils from the Diocesan Boys’ School in Hong Kong, he says.

A 20-minute drive to the northeast of Noyelles is Crécy-en-Ponthieu, where another historic battlefield can be found, although this one dates from 1346 and the beginning of the 100 Years War, fought between France and England.

The hamlet has a new museum and visitors’ centre – built during the pandemic and inaugurated in March – in which the victory of the feared English archers is brought to life in model recreations and animated films.

To explore the Somme estuary and bay itself, I base myself at the picture-postcard fishing port of Saint-Valéry. Its medieval citadel and majestic Gothic church are surrounded by towering city walls with panoramic views all the way to Le Crotoy.

Victorian mansions line the promenade along the sea dyke, recalling the era when Saint-Valéry was a favourite retreat for the writers Victor Hugo, Jules Verne and Colette, while the seascapes inspired Edgar Degas (whose View of Saint-Valéry-sur-Somme, 1896-98, is on display at The Met museum, in New York) and Georges Seurat (Vue sur Le Crotoy, 1889).

With the town’s fishing boats bringing in freshly caught sole, turbot and scallops, fish is always on the menu at the grandiose turreted mansion Le Relais Guillaume de Normandy, named in honour of William the Conqueror, but the speciality here is mussels, harvested on nearby beaches.

The perfect place for a bowl of mussels cooked in white wine with crispy frites is La Terrasse, a welcoming bistro right on the waterside.

The road that runs round the whole of the estuary may be narrow, but there is a bike track running alongside and bicycles are easily hired. However, I prefer to explore the area on foot.

From Saint-Valéry, I follow the long boardwalk along the southern bank of the estuary as far as Cap Hornu, where there is a lively buvette, a bar on the beach, next to kayak clubhouses. I then head through a windswept landscape to the southern tip of the bay, Le Hourdel.

The quayside here is lined with ruddy-faced retired fishermen, fishmongers stationed outside their refrigerated vans and local families waiting to buy some of the day’s catch as soon as the boats dock – or just to enjoy a spectacular sunset.

To cross the estuary, from Saint-Valéry to Le Crotoy, I join a low-tide nature walk, which must be led by a professional guide as the sea can rush quickly into the bay once the tide turns.

Although the terrain looks flat, almost like a desert, this is actually a strenuous three-hour trek. On the Saint-Valéry quayside, we are given Wellington boots, which are necessary to clamber through the gulleys and up the steep grassy dunes, often sinking into thick, cloying mud.

As we walk, the guide identifies the birds flying above and the edible sea-ferns, or salicornes, growing wild in the grass.

The view as we approach Le Crotoy is dominated by a 19th century hotel looking out over the bay. Called Les Tourelles because of its tall towers, it resembles a fashionable holiday retreat you might find in the Hamptons, on New York’s Long Island.

Les Tourelles’ terrace has the ultimate view over the bay and is a great spot for sunset cocktails or a romantic dinner. It’s also a perfect spot in which to reflect on a visit to the not-so-sombre Somme.