Indonesia–Timor-Leste border

One island, two empires

Timor is the last island at the eastern end of the chain of the Sunda Islands and the closest to Australia. It is about 500 km long and at most 100 km wide, with a mountain range down its length whose peaks reach nearly 3,000 metres.^[1] By the early 1900s Portugal held the eastern part, about 19,000 km² with some 300,000 people. The Netherlands held the west, about 20,000 km² with 131,000 people counted in 1907, except for the “Kingdom of Oecusse and Ambeno” on the northwest coast, which was Portuguese and surrounded by Dutch land on every side but the sea.^[1]

A treaty signed at Lisbon on 20 April 1859, and ratified in 1860, divided the island through the middle. It left two pockets on the wrong side: a Dutch enclave, Maucatar, among Portuguese territory, and the Portuguese enclave of Oecusse among Dutch territory in the west. The treaty said the Oecusse enclave took in the state of Ambeno wherever the Portuguese flag flew, Oecusse itself, and Noimuti.^[1]

In a convention signed at Lisbon on 10 June 1893, the two governments agreed to mark their possessions “in a clearer and more exact way” and to get rid of the enclaves. A joint commission went out to the island and in 1898–99 agreed most of the line, but disagreements remained both on the main border and around Oecusse.^[1]

The 1904 convention

A conference at The Hague from 23 June to 3 July 1902 worked through the disagreements. Its draft became a convention signed at The Hague on 1 October 1904.^[1] The Netherlands gave Maucatar to Portugal, and Portugal gave Noimuti, Tahakay and Tamiru Ailala to the Netherlands.^[1] Oecusse stayed Portuguese, and it is still a separate piece of Timor-Leste today.^[2]

The convention described the main border from north to south. It starts at the mouth of the Mota Biku (Silaba) on the north coast and ends at the mouth of the Mota Masin on the south coast. In between it follows the thalweg (the deepest channel) of a long chain of rivers, crossing from one to the next over named hilltops, and once past “the big tree named Halifea” and “the big stone named Fatu Rokon”.^[1] Oecusse's boundary starts at the mouth of the Noel Besi in the west, runs inland along rivers and summits, and comes back down the Noel Meto to the coast in the east.^[1] The convention also let people of both sides use the boundary rivers freely, except for carrying weapons and ammunition.^[1]

One stretch was left unfinished. On Oecusse's eastern side the convention drew only a rough line: up a stream called the Oè Sunan, through Nipani and Kelali, to the source of the Noel Meto. It asked for this line to be surveyed and marked on the ground as soon as possible.^[1]

“Proceeding from the mouth of the Noel (river) Besi, from where the summit of Pulu (Island) Batek can be sighted, on a 30°47′ NW astronomical azimuth, following the thalweg of the Noel Besi, that of the Noel Nima and of the Bidjael Sunan up to its source”^[7]

Arbitration over a missing river

Surveyors from both countries began marking Oecusse's eastern border in June 1909. They walked up the Noel Meto from the coast and placed a marker at its source.^[1] Further south, on 17 June 1909, they reached the spot on the Noel Bilomi where the 1904 map showed the Oè Sunan flowing in. They found two streams coming in from the north, and neither was called the Oè Sunan.^[1] The Dutch delegates wanted to run the line north from the point shown on the maps. The Portuguese delegates pointed to a river called Oè Sunan further east and wanted the line to go that way. The commission surveyed both lines and left the choice to the governments.^[1]

After years of letters between the two foreign ministries, the Netherlands and Portugal agreed at The Hague on 3 April 1913 to hand the question to an arbitrator of the Permanent Court of Arbitration. They chose Charles Édouard Lardy, the Swiss minister in France.^[1] The Netherlands argued that the stream marked “Oè Sunan” on the 1899 and 1904 maps had simply been given the wrong name. Locally it was called the Kabun or the Leos, the Dutch said, but it was the stream the two sides had meant to follow.^[1]

His award, signed in Paris on 25 June 1914, upheld the Dutch reading. The line from the Noel Bilomi to the source of the Noel Meto was to be surveyed on the 1:50,000 map the Dutch government had submitted.^[1] Together with the 1904 convention, it is the colonial line the two countries use today.^[3]

From provincial line to international border

Indonesia declared independence from the Netherlands in 1945, and today it holds the west of the island.^[3][2] On 22 December 1975 the UN Security Council deplored “the intervention of the armed forces of Indonesia in East Timor” and called on all states to respect East Timor's territorial integrity.^[8] Indonesia governed East Timor until 1999, a period Timor-Leste's government describes as Indonesian military occupation.^[3] During those years the colonial line was a boundary between two Indonesian provinces, East Nusa Tenggara and East Timor, and a provincial boundary pillar was set up in 1992 at Naktuka, at the western end of Oecusse.^[7]

On 30 August 1999 East Timorese voted in a UN-run ballot on whether to accept special autonomy within Indonesia. 344,580 people, 78.5% of the vote, rejected it, choosing a transition towards independence.^[9] More than 250,000 people then fled to West Timor, on the Indonesian side of the border. Over the next three years more than 220,000 went back, and when their refugee status ended on 1 January 2003 about 30,000 were still in West Timor.^[10]

Timor-Leste's independence was restored on 20 May 2002, and the two countries soon began discussing their land border. They agreed to base it on the 1904 convention and the other colonial documents.^[2] This follows the principle of uti possidetis juris, under which a new state keeps the borders of the territory it came from.^[7]

The last few kilometres

A Provisional Agreement on the land boundary, signed on 8 April 2005, settled most of the line, and a first addendum followed on 21 June 2013.^[2][3] What was left were short stretches where the old treaty text and the ground disagree. Two of them, the Noel Besi at Citrana and Bidjael Sunan near the village of Oben, are named in the opening clauses of the 1904 convention's description of Oecusse.^[1][6]

The Noel Besi–Citrana segment is at the western end of Oecusse, next to Indonesia's Kupang Regency. The land at stake, known as Naktuka, is a fertile river delta of about 1,069 hectares.^[7] The 1904 text puts the border's start at a river mouth sighted from Batek Island on a set compass bearing. Indonesia says the Noel Besi is the large river on the east side of the delta. Timor-Leste says the treaty map, the bearing and the older maps all point to the smaller channel on the west side, now called the Nono-tu-i-nan.^[7] In 2022 researchers were told that about 110 families holding Timor-Leste identity cards lived and farmed in Naktuka.^[7] At Bidjael Sunan–Oben the disputed land covers 142.7 hectares along 2.6 km.^[7]

On 22 July 2019 Xanana Gusmão, Timor-Leste's chief land border negotiator, and Indonesia's coordinating minister for security, Wiranto, signed “Agreed Principles” in Jakarta to settle both segments.^[6][2] Wiranto said that “all land boundary negotiations are in principle complete,” and the principles were to become a second addendum to the 2005 agreement.^[11] Timor-Leste had hoped to finish the land border in 2020, but COVID-19 delayed the meetings.^[2] In January 2024 President Joko Widodo and Prime Minister Xanana Gusmão again committed to completing the negotiations.^[12] In September 2025 Indonesia's border agency told parliament that three segments were still unsettled: Noelbesi–Citrana, Subina–Oben and Humamania–Pasabe.^[4] The land border also matters at sea: its end points on the coast have to be fixed before the two countries can draw a maritime boundary.^[2]

On the main border, Indonesia's Mota’ain post faces Batugade in Timor-Leste.^[6] Indonesia rebuilt the Mota’ain post in Belu Regency, and President Joko Widodo opened it on 28 December 2016, when he also visited the Motamasin post in Malaka Regency further south.^[5]