A judge sent former Portuguese prime minister Jose Socrates to prison while the ex-leader fights accusations of corruption, money-laundering and tax fraud.
The judge decided after an initial hearing there was sufficient police evidence to keep Socrates in custody on preliminary charges of wrongdoing, a court statement said.
His lawyer, Joao Araujo, said his client denies the charges and would appeal against the custody decision.
Under Portuguese law, the public prosecutor will now investigate further before presenting formal charges, a process that could take more than six months.
A magistrate will then decide whether to put Socrates on trial. The crimes carry a maximum sentence of 21 years.
Socrates was Portugal's centre-left Socialist prime minister from 2005 to 2011. He was detained by police after arriving at Lisbon airport late on Friday and has been in jail since. Three other suspects were also arrested as part of the investigation.
Officials refused to provide details, because a judicial secrecy law forbids the disclosure of information from ongoing investigations
Local media reported that Socrates, 57, is suspected of amassing a €20 million fortune by taking bribes to favour companies during his time in power. The reports cited unidentified police sources.
One of the other suspects, Carlos Santos Silva, is said to be a long-time friend of Socrates. His construction company flourished during Socrates's time in power.
Investigators reportedly suspect that Socrates's alleged illicit gains were kept in a Swiss bank account held by Santos Silva.
The suspicions swirling around Socrates have generated Portugal's third major scandal in four months.
Taken together, the allegations have shaken public faith in the country's political and business elite.
Last summer saw the collapse of the country's largest and oldest listed bank, Banco Espirito Santo, and the arrest of its chief executive Ricardo Espirito Santo Salgado, the patriarch of one of Portugal's most distinguished families, on charges of fraud, forgery and money-laundering.
Earlier this month, police detained the head of the country's immigration service and several other senior officials in a corruption investigation centred on the granting of residence permits to wealthy investors from outside the EU.
The scandal involving Socrates has appalled the austerity-hit Portuguese.
Socrates requested a €78 billion international bailout for Portugal in 2011 when the country was engulfed by a debt crisis that hit countries sharing the euro currency.
The bailout, which contributed to Socrates's election defeat a few months later, brought pay and pension cuts, steep tax increases and a spike in unemployment.
Socrates made his name as a liberal moderniser. He introduced abortion on demand and gay marriage in his mostly Roman Catholic country.
He also put Portugal at the forefront of Europe's drive to adopt renewable energy.