Turkey on Sunday votes in a tightly-contested referendum on expanding the powers of President Recep Tayyip Erdogan that will shape its political system for the next generation and determine the key NATO member's future relationship with the West.
A crossroads in the history of the modern republic founded amid the ashes of the Ottoman Empire in 1923, the referendum is seen as too close to call, with the country polarised between the 'Yes' and 'No' camps.
Critics fear victory in the referendum on a new constitution creating an executive presidency would pave the way for one-man rule and allow Erdogan to tear up the secular principles established by Turkey's founder Mustafa Kemal Ataturk.
But supporters say that the system -- which would eliminate the post of prime minister -- is needed to eliminate the political crises that marred the 1980s and 1990s before the rise of Erdogan's Islamic-rooted Justice and Development Party (AKP).
The vote is also shadowed by the failed military coup against Erdogan in July that was rapidly followed by a state of emergency that remains in place and has seen tens of thousands of people arrested.
- 'Could go either way' -
From the Hatay region on the border with Syria to Izmir just across the Aegean from Greece, Erdogan has criss-crossed the country in an energetic quest for votes, seeking to rouse supporters with his trademark charisma.
He roars that a 'No' vote would play into the hand of Turkey's enemies such as the outlawed Kurdistan Workers' Party (PKK) and the group of US-based preacher Fethullah Gulen, blamed for the coup plot.
Backed by considerably more modest resources and lacking any clear single leader, the 'No' campaign has still managed to stay competitive, bringing together a mixture of secularists, anti-Erdogan Kurds and some nationalists.
"The vote could still go either way," Asli Aydintasbas, senior policy fellow at the European Council on Foreign Relations, told AFP, adding that whatever the outcome the winning side would only poll in "the low 50s".
Analysts say the key is the nationalist vote, which is split between those supporting Nationalist Movement Party (MHP) leader Devlet Bahceli, who backs the proposed new system, and a dissident faction led by the forceful Meral Aksener which rejects it.
Also crucial will be Turkey's Kurds, who make up at least one fifth of the population and millions of whom, especially from more conservative families, have in the past backed Erdogan but may be put off by the AKP's alliance with the MHP.
- 'Most power since 1950s' -
The new system, which would replace a constitution drawn up in the wake of the 1980 military coup, would create a single powerful bureaucracy within the presidency, including vice president posts instead of a prime minister.
It would come into force in 2019, when presidential and parliamentary elections would be held simultaneously and theoretically allow Erdogan two more mandates to stay in power to 2029.
"The new system would endow the Turkish president with more power than any civilian leader has enjoyed in that nation since the end of Ismet Inonu's presidency in 1950," said Alan Makovsky a Senior Fellow at the Center for American Progress, referring to Ataturk's successor and right-hand-man.
- 'Decision for EU' -
But the implications could be just as far reaching for Turkey's relationship with the European Union, which Ankara has sought to join since the 1960s in a continually stuttering process.
Tensions with Brussels have soared after Erdogan blasted EU capitals for behaving like the Nazis in preventing Turkish ministers from holding pre-election rallies.
The rhetoric of Erdogan, who has described Europe as both a "rotting continent" and the "centre of Nazisim", has raised questions over whether the Turkish membership bid saga is crashing to an unhappy end.
The president has also repeatedly vowed to "without hesitation" sign any bill passed by parliament to bring back capital punishment, a move that would drive the final nail into its membership aspirations.
Marc Pierini, visiting scholar at Carnegie Europe, said EU leaders will have a "decision to make on both the style and substance of future relations with Turkey".
- 'Say 'No' to fear' -
Some 47,000 people are being held in jail under the state of emergency imposed after the coup, a magnitude whose scale has raised alarm in Europe that the crackdown has gone well beyond the plotters themselves.
Meanwhile 141 journalists are being held behind bars, including prominent writers with the opposition Cumhuriyet daily, according to the P24 media freedom website.
Also held since November 2016 are Selahattin Demirtas and Figen Yuksekdag, the co-leaders of the pro-Kurdish Peoples' Democratic Party (HDP), the third largest party in the Turkish parliament, on accusations of supporting the PKK.
The HDP says Demirtas is being held to avenge his opposition to the new system and the 'No' campaign would have been transformed by the presence of the only Turkish politician who rivals Erdogan's rhetorical skills.
Accusing the AKP of creating a "climate of fear", Demirtas said in a message from prison: "I invite everyone to defeat this fear, go to the ballots and say 'No' to fear."