It will be the country's first trial of a suspected Isis militant deployed to Germany from Syria during the chaotic 2015 refugee influx - in contrast to "lone wolf" attacks or plots by extremists who were radicalised elsewhere.
The defendant, 20-year-old Syrian national Shaas al-Mohammad, allegedly fought with the Islamist militia in his war-torn homeland for two years before arriving in Germany as a refugee in August 2015.
Dressed in a blue pullover and a black cap, Mohammad kept his eyes on his interpreter and remained silent as his lawyers tried in vain to convince the judge to hold the hearings behind closed doors due to his young age.
Two police trucks were parked outside the entrance, with officers armed with machine guns guarding the proceedings.
Mohammad was standing trial at a special state security court in Berlin on charges of membership of a foreign terrorist organisation, which carries up to 10 years in jail, and military weapons law violations.
The trial comes just over two weeks after an Isis extremist from Tunisia ploughed a truck through a Berlin Christmas market in an attack that killed 12 people.
Prosecutors claim the defendant joined the jihadist group as a teenager in mid-2013, taking part in combat operations, handling an AK-47 assault rifle and supplying food to fighters.
He arrived in Germany near the peak of a mass influx of people fleeing Syria, Iraq and other crisis-torn countries that brought almost 900,000 asylum seekers to Europe's biggest economy in 2015.
He allegedly stayed in "close contact" with Isis and repeatedly visited the German capital until February 2016 to scout out landmark targets and busy tourist sites for an attack.
Among the suspected targets were the area around the glass-domed Reichstag building that houses the lower house of parliament, the nearby Brandenburg Gate monument and the busy shopping square Alexanderplatz.
He then allegedly "passed the information about the potential attack targets onto his contacts at Isis", said the court in a statement.
"In addition, he arranged to send at least one person to Syria as a fighter and offered his services as a contact person for potential attackers in Germany," it added.
But Mohammad only admitted to selling supplies to Isis members, and denied having any contact with anyone of consequence in the jihadist group.
The young Syrian was arrested on March 22nd last year and has been in pre-trial detention since. The court has set 25 hearings until April.
Germany has been shocked by a spate of Isis-claimed attacks, and some foiled plots, that the far-right Alternative for Germany have blamed on the open-door refugee policy of Chancellor Angela Merkel, leading to them gaining in the polls.
In some cases last year, the jihadists were home-grown, while others were migrants and refugees.
More attacks are feared when some of the 400-odd German jihadists still in Syria and Iraq return home.
In June last year, police arrested three Syrian men over an alleged plan to use guns and suicide vests in an Isis attack in Düsseldorf.
In July, a 17-year-old Afghan refugee wounded five people in an axe rampage on a train before police shot him dead.
Days later a 27-year-old Syrian blew himself up outside a music festival, wounding 15 people.
In October, police say they prevented an attack on a Berlin airport by a Syrian refugee, 22-year-old Jaber al-Bakr.
Al-Bakr evaded a police raid but was caught by Syrian compatriots soon after and handed over to police. Two days later, he was found hanged in his cell, sparking a scandal over the security lapse in custody.
December saw the worst Isis-claimed attack when Tunisian Anis Amri, 24, drove a hijacked truck into a packed Berlin Christmas market.
He killed 12 people, including the lorry's registered Polish driver, and was shot dead four days later in Italy after firing first at police there.
Germany's domestic security service estimates that the number of radical Islamists in Germany rose above 9,000 last year, from some 3,800 in 2011.
About 550 of them are considered dangerous and capable of a violent attack.