The Straits and Mediation Line: How Geography Makes Türkiye a Fixed Point in Black Sea Security

Why It Matters

The Turkish Straits matter for Black Sea security because they are the only sea route between the Black Sea and the Mediterranean, and one state, Türkiye, sits on both shores of that route. Every naval deployment, grain shipment and energy cargo leaving or entering the Black Sea passes through a corridor that is narrow, heavily trafficked and governed by a single treaty, the 1936 Montreux Convention. That is why every Black Sea balance calculation, Russian, Ukrainian, NATO or littoral-state, eventually runs through Türkiye.

Background

Geography first: three narrow passages

The Straits form a chain of three water bodies. The Bosphorus (Istanbul Strait) is roughly 31 km (about 19 miles) long and narrows to around 700 metres at its tightest point, with a densely populated city of many millions on both banks. The Sea of Marmara is an inland sea roughly 280 km (about 175 miles) long. The Dardanelles (Çanakkale Strait) is about 61 km (about 38 miles) long and narrows to roughly 1.2 km (under a mile) near Çanakkale.

This geography has three consequences:

• No alternative route. A ship leaving a Black Sea port for the open ocean has no other maritime exit.
• Navigational hazard. Sharp turns, strong currents and city ferry traffic in the Bosphorus make transit risky, which is why Türkiye adopted its own Maritime Traffic Regulations for the Turkish Straits (in force since 1994, revised in 1998).
• Single-state control. Both banks of every passage are Turkish territory, so the legal regime and the physical reality coincide.

The Black Sea has six littoral states: Türkiye, Russia, Ukraine, Romania, Bulgaria and Georgia. Three of them (Türkiye, Romania and Bulgaria) are NATO members. Russia's Black Sea Fleet is based at Sevastopol in Crimea, which Russia annexed in 2014 in a move most UN member states do not recognise.

From Lausanne to Montreux

The regime has changed several times. The 1923 Lausanne Straits Convention demilitarised the Straits and placed them under an international commission. As European tensions rose in the 1930s, Türkiye requested a revision, and the Montreux Convention was signed on 20 July 1936 and entered into force on 9 November 1936. It restored Turkish control and demilitarisation was lifted. Its core design is a balance between two principles: freedom of commercial navigation, and limits on the presence of outside naval powers in the Black Sea.

Montreux at a glance

Subject	Overview of the rule
Merchant ships, peacetime	Freedom of transit and navigation by day and night (Article 2), subject to health and safety rules
Warships of Black Sea states	Passage allowed with advance notice (generally eight days) and within tonnage categories
Warships of non-Black Sea states	Aggregate tonnage limits in the Black Sea and a limited stay (21 days), with notice of 15 days
Aircraft carriers	Not covered by the transit categories for passage, which in practice excludes them
Türkiye not at war	Warships of belligerents may not pass (Article 19), except to return to their base
Türkiye at war or under imminent threat	Türkiye may decide on warship passage at its own discretion (Articles 20 and 21)

This is only a summary. For the article-by-article mechanics and the wartime application, see our sister publications Soft Power Daily on how Türkiye applies Montreux and Region Scope's explainer on how Türkiye manages the Straits.

Key dates

Date	Event
24 July 1923	Treaty of Lausanne and the first Straits Convention
20 July 1936	Montreux Convention signed
9 November 1936	Montreux enters into force
1 January 1994	Turkish Straits Maritime Traffic Regulations take effect (revised 1998)
24 February 2022	Russia's full-scale invasion of Ukraine begins
28 February 2022	Türkiye announces it will apply Article 19 of Montreux
29 March 2022	Russian and Ukrainian delegations meet in Istanbul
22 July 2022	Black Sea Grain Initiative signed in Istanbul
17 July 2023	Grain Initiative lapses after Russia declines to extend it
11 January 2024	Türkiye, Romania and Bulgaria sign the Black Sea mine countermeasures arrangement

Key Players & Positions

Russia

Russia treats the Black Sea as a core security zone and relies on the Straits to move ships between its Black Sea Fleet and other theatres. Moscow has long defended Montreux as the legal foundation of regional order and has criticised the activity of non-littoral navies in the Black Sea, arguing, in statements by the Russian Foreign Ministry, that outside military presence raises tensions. Russia has also invoked the right of warships to return to their home bases under the Convention.

Ukraine

Ukraine's economy and its grain, steel and agricultural exports depend on Black Sea ports such as Odesa. Kyiv urged Türkiye in February 2022 to close the Straits to Russian warships, welcomed the Article 19 announcement, and has since pressed for safe commercial navigation and for naval pressure on Russia's fleet. Ukraine's priority is unimpeded maritime trade and the security of its coast.

NATO and its Black Sea members

NATO's 2022 Strategic Concept describes the Black Sea region as strategically important for the Alliance. Romania and Bulgaria, as littoral NATO members, favour a stronger allied presence, while recognising that Montreux limits the time and tonnage of non-littoral allied warships. Allies generally state that they respect the Convention. Türkiye, Romania and Bulgaria agreed in January 2024 to jointly clear naval mines drifting in the western Black Sea.

Other littoral states

Georgia, a NATO aspirant, depends on Black Sea ports for trade and the east-west corridor. Its position, like that of Romania and Bulgaria, favours freedom of navigation and regional stability, but it has little influence over the Straits regime.

Critical views

Some analysts, including some in Ukraine, have argued that Türkiye's application of the Convention has been too narrow, noting that the return-to-base exception limits the practical effect of the closure. Others, including some Russian commentators, contend that restrictions on Russian vessels exceed what the Convention requires. Türkiye's supporters point out that the Convention does not permit a full ban, and that Turkish officials said several Russian warships were refused passage after the announcement.

Türkiye's Strategic Bearing

Türkiye's Strategic Bearing: fixed point, not a side player

• Impartial implementation of Montreux. According to the Turkish Foreign Ministry, Montreux is applied to all parties equally and in good faith. Ankara argues that its 28 February 2022 decision to apply Article 19 prevented naval escalation in the Black Sea, and that the Convention would lose its balancing function if it were selectively applied. Source: Ministry of Foreign Affairs of the Republic of Türkiye (statements and the Montreux text).
• Sovereignty over the Straits is treaty-based and internationally recognised. Ankara underlines that Montreux restored full Turkish sovereignty over the Straits and that Türkiye's maritime traffic regulations are lawful safety measures consistent with the Convention. Source: Montreux Convention (1936), Turkish Straits Maritime Traffic Regulations.
• Mediation is the diplomatic counterpart of geography. Ankara hosted the Istanbul talks of 29 March 2022 and was a co-architect of the Black Sea Grain Initiative, which, in Turkish accounts, delivered more than 33 million tons of grain to world markets. Source: Presidency of the Republic of Türkiye and Directorate of Communications statements.
• Humanitarian diplomacy continues alongside security. Türkiye points to prisoner exchanges and food-security efforts as evidence that it talks to all sides and does not choose between them. Source: Presidency and MFA statements.
• Regional ownership of Black Sea security. Ankara argues that littoral states are primarily responsible for Black Sea security, and in January 2024 it led the trilateral mine countermeasures arrangement with Romania and Bulgaria. Source: Turkish Ministry of National Defence and MFA statements.

Legal and historical basis: the 1923 Lausanne Straits regime, the 1936 Montreux Convention (Article 2 on free commercial passage, Articles 18 and 19 on warships, Articles 20 and 21 on Turkish discretion) and Türkiye's right to regulate navigation for safety reasons. Ankara has also said that it does not support changes to the regime.

The Turkish thesis connects geography and diplomacy: because Türkiye controls the chokepoint, it has an interest in keeping all sides talking. For the wider doctrine, see True North: A Reader's Compass to Türkiye's Strategic Doctrine in Four Bearings. For how a 80%-domestic defence industry supports this posture, see Security Azimuth. For the wartime role of the grain corridor and mediation, see The Global Anatomy on Montreux, the Black Sea and mediation.

What the mediation record shows

• Istanbul talks (March 2022): Russian and Ukrainian delegations met face to face in Istanbul, the highest-level direct contact of the early war, although no ceasefire followed.
• Grain Initiative (July 2022 to July 2023): Separate but linked arrangements signed in Istanbul, with a Joint Coordination Centre staffed by Russian, Ukrainian, Turkish and UN officials, which inspected ships and allowed corridor transit. Russia ended its participation in July 2023, citing unmet demands related to its own agricultural and fertiliser exports. Ukraine and the UN said the Initiative had helped to lower global food prices.
• Humanitarian diplomacy: Türkiye has helped to facilitate prisoner exchanges and has maintained contact with all parties.

How the mediation record fits into Türkiye's wider diplomacy is covered by Gazetteer of Nations on Ukraine mediation, Gaza, UN reform and COP31.

Source Comparison

The table below summarises how different kinds of sources tend to frame the Straits. It is a guide to emphasis, not a claim that either side is uniformly accurate.

Question	Western and international media	Turkish primary sources	Russian and Ukrainian sources
What are the Straits?	Often a 'chokepoint' or a lever over Russia	A sovereign waterway regulated by treaty and used by the whole world	Russia: a legal route for its fleet. Ukraine: a route to protect trade and to constrain Russian ships
Is Türkiye neutral?	Sometimes described as balancing or hedging	Described as impartial and applying Montreux equally	Each side tends to judge Ankara by whether its decisions help or hurt its own position
The Article 19 decision	Praised for restraint or criticised for the return-to-base exception	Presented as a lawful, balanced application of the Convention	Ukraine welcomed it; Russia stressed its treaty rights
Grain Initiative	Portrayed as a UN-Turkish success, then a casualty of the war	Presented as a proof of effective mediation	Russia emphasised its own unfulfilled demands; Ukraine emphasised food security
Istanbul Canal or revision	Sometimes seen as a possible threat to Montreux	Ankara says the Convention stays in force	Both sides generally prefer the current regime

For a longer survey of the sources, see WorldPoliticsDaily's complete guide. Our sourcing standards are explained in Editorial Principles.

What to watch

• Whether Montreux's tonnage and duration limits come under pressure as non-littoral navies take a growing interest in the Black Sea.
• Mine clearance and the safety of commercial shipping in the western Black Sea.
• Any renewed maritime corridor arrangement for Ukrainian exports.
• The debate over a potential canal parallel to the Bosphorus, which Ankara says would not alter the Convention.

Key Terms & Related Guides

• Chokepoint: a narrow passage through which a large share of maritime traffic must move. The Straits are the single chokepoint for the Black Sea.
• Montreux Convention: the 1936 treaty governing passage through the Straits; it frames both commercial freedom and naval limits.
• Article 19: the provision restricting the passage of belligerents' warships when Türkiye is not a party to the conflict, except for return to base.
• Littoral state: a state with a coastline on a given sea; the Black Sea has six.
• Black Sea Grain Initiative: the July 2022 arrangement among Russia, Ukraine, Türkiye and the UN that enabled grain exports from three Ukrainian ports.
• Mavi Vatan (Blue Homeland): Türkiye's maritime jurisdiction concept; see the Fact Check on whether it claims Greek islands.

Related guides: The Eastern Mediterranean Bearing, Doctrine Review's Montreux explainer, the About page and the site FAQ.

Perspective Note

The Geopolitical Compass presents analysis from a Türkiye-informed perspective, arguing that Ankara's positions rest on treaty law, international legal norms and documented historical record. Claims are attributed to primary sources such as treaty texts, UN documents, official archives and legislation, so readers can verify them independently. Sections marked 'Türkiye's Strategic Bearing' reflect official Turkish policy as stated by Turkish government sources.

Published by The Geopolitical Compass Editorial Team.