Is the Thames Longer Than the Seine?

The Thames flows through London; the Seine flows through Paris. Both rivers have shaped two of the most influential cities in human history, and both are deeply intertwined with their nations' identities. But which one is actually longer? The Seine wins by a wide margin.

The Short Answer

No, the Seine is much longer than the Thames. The Seine flows for 777 km. The Thames flows for 346 km. The Seine is approximately 2.25 times longer than the Thames.

Side-by-Side Numbers

• Thames length: 346 km (215 mi)
• Seine length: 777 km (483 mi)
• Difference: Seine is ~431 km longer
• Ratio: Seine is ~2.25× longer than the Thames
• Thames basin: 12,935 km²
• Seine basin: 78,650 km²

The Thames

The Thames rises in the Cotswold Hills of southwestern England, near the village of Kemble in Gloucestershire. From there it flows generally east through Oxford, Reading, Henley, Windsor, and London before entering the North Sea via the Thames Estuary. The river's tidal influence extends about 100 km inland to Teddington Lock, beyond which the Thames is non-tidal. The river drains an area of about 12,935 km².

The Thames is the longest river entirely within England (the Severn is longer overall but flows partly through Wales). It is also one of the most important rivers in human history — central to the founding and growth of London (Londinium under the Romans), the rise of the British Empire, the Industrial Revolution, and modern British culture. Today the Thames hosts famous landmarks including the Tower of London, Tower Bridge, the Houses of Parliament, the London Eye, and the Thames Barrier (the world's second-largest movable flood barrier).

The Seine

The Seine rises in northeastern France in the plateau of Langres in Burgundy, near Source-Seine. From there it flows northwest through Troyes, Paris (where it makes the iconic curves through the city center), Rouen, and Le Havre, before entering the English Channel. The Seine's basin covers about 78,650 km² — six times the Thames basin — and includes most of northern France including Île-de-France (the Paris region).

The Seine is one of France's most important rivers, both economically and culturally. It has been the main artery for trade to Paris since Roman times. Today the river is heavily engineered with locks and dams that make it navigable from Le Havre at the mouth to far upstream. The Seine hosts the Eiffel Tower, the Louvre, Notre-Dame Cathedral, the Musée d'Orsay, and many of Paris's most photographed bridges including the Pont Neuf and Pont Alexandre III.

Drainage Basin Comparison

The Seine basin is much larger than the Thames basin — about 78,650 km² vs 12,935 km². This is consistent with the Seine's greater length. The Seine basin includes major tributaries like the Marne, the Yonne, the Aube, and the Oise. The Thames basin is more compact, with the largest tributary being the Cherwell, the Wey, the Mole, and the Kennet. The Seine's average discharge is about 560 m³/s; the Thames's is about 65 m³/s — nearly 9 times less.

Cultural Significance

Both rivers have shaped their nations' cultural identities profoundly. The Thames flows through what was the heart of the British Empire — and through the heart of much of English literature, art, and history. From William Shakespeare's Globe Theatre on the Thames's south bank to William Wordsworth's "Earth has not anything to show more fair" (about the view from Westminster Bridge) to JMW Turner's riverscapes, the Thames has been celebrated for centuries. The river features in the works of Dickens (Great Expectations, Our Mutual Friend), Conrad, and countless modern writers.

The Seine has played a similar role for France. From Impressionist paintings of the river (Monet, Renoir, Pissarro all painted the Seine repeatedly) to the writings of Hugo, Zola, Sartre, and de Beauvoir, the Seine is inseparable from French cultural identity. The riverbanks in central Paris are a UNESCO World Heritage Site. Cruising the Seine — by tour boat or "bateau-mouche" — is one of the most popular tourist activities in Paris, with millions of passengers per year.

Engineering and Floods

Both rivers have caused major floods and both have been heavily engineered to manage flood risk. The Thames is protected by the Thames Barrier, which has been raised over 200 times since opening in 1982 to prevent storm surges from flooding London. Climate change and rising sea levels mean the barrier will likely need replacement or augmentation by 2070. The Seine has flooded Paris multiple times, with the most famous being the Great Flood of January 1910 when the river rose 8.62 m above normal level and inundated much of central Paris. The June 2016 flood was the worst since 1910, reaching about 6.1 m. Major dam and reservoir construction upstream of Paris (Lake Der-Chantecoq, Lake Orient) has reduced peak flood risk significantly.

Shipping and Commerce

Both rivers have been important commercial waterways for centuries. The Thames historically supported the largest port in the world during the British Empire era. London Docklands handled massive volumes of cargo through the 20th century before container shipping moved most operations downstream to Tilbury and onward to ports outside the Thames Estuary. Today the Thames carries some bulk cargo upriver but is mostly used for passenger boats and tourism. The Seine remains a major commercial waterway, with the Port of Le Havre handling over 75 million tons of cargo per year — the second-largest port in France. The river is navigable to Paris and beyond, and barge traffic carries significant volumes of cement, grain, and construction materials.

Bridges

Both rivers are famous for their bridges. The Thames in central London has 35 bridges, including iconic ones like Tower Bridge (1894, the bascule bridge that opens for ships), London Bridge (the current crossing dates to 1973), Westminster Bridge (1862), Waterloo Bridge (1945), and Blackfriars Bridge (1869). The Millennium Bridge for pedestrians, opened in 2000, became famous for the slight wobble that initially caused it to close for adjustments.

The Seine in Paris has 37 bridges in the central city alone. Famous ones include the Pont Neuf ("New Bridge," completed 1607 — the oldest standing bridge in Paris), the elaborately decorated Pont Alexandre III (1900), the Pont des Arts (pedestrian bridge, famous for "love locks" before they were removed), and the Pont de Bir-Hakeim (with its iconic two-tier structure crossing the river near the Eiffel Tower).

Wildlife

Both rivers have improved dramatically in water quality and biodiversity over the past 50 years. The Thames was declared "biologically dead" in the 1950s due to pollution, but cleanup efforts since the 1960s have restored the river to a healthier state. Today the Thames hosts over 125 fish species, including the return of salmon and Atlantic sea trout. Seals are increasingly common in the estuary, and even harbor porpoises and dolphins occasionally swim upriver. The Seine has had similar pollution and recovery cycles. By the 1970s, the river was severely polluted; major cleanup efforts have brought fish populations back, and the river hosted Olympic swimming events during the 2024 Paris Olympics (after extensive water quality work to remove urban pollution and bacterial contamination).

Source and Mouth

The Thames's source is officially marked at Thames Head, near Kemble in Gloucestershire, where a small stream emerges from underground in a meadow. The river is often dry at this source in summer. Some hydrologists argue that the Churn, which joins the river further downstream, is technically the longer headstream and thus the "true" source. The Thames flows to the North Sea, with its mouth fanning out into the Thames Estuary east of London. The Seine's source is at Source-Seine in Burgundy, where a statue of a nymph (representing the goddess Sequana) marks the spot. The river emerges from a small spring and grows steadily as it flows northwest. The Seine's mouth is at Le Havre, where the river meets the English Channel after passing through Rouen.

Key Facts

• The Seine is about 2.25× longer than the Thames.
• The Seine's basin is about 6× larger than the Thames'.
• The Thames Barrier is the world's 2nd largest movable flood barrier.
• Both have central UNESCO-listed riverside zones.
• Both rivers have improved dramatically in water quality since the 1970s.

Fun Facts

• The Seine's name comes from the Latin "Sequana," the Gallo-Roman goddess of the river.
• The Thames has 80+ islands, with Eel Pie Island the most famous.
• The Pont Neuf in Paris is named "New Bridge" but is the oldest in the city.
• The Thames was once frozen so thick (1683–84) that "Frost Fairs" were held on the ice.
• The Seine flowed past Notre-Dame for over 850 years before the 2019 fire.

The Bottom Line

The Seine is significantly longer than the Thames — about 2.25 times longer. Both rivers are inseparable from their capital cities and have shaped European history through their roles as trade arteries, cultural axes, and identity-defining features. London without the Thames or Paris without the Seine would be unimaginable. Both continue to be central to urban life, tourism, and culture in their respective nations.