Tunisian national Anis Amri, 24, hijacked a truck on December 19 last year and slammed it into a crowd of shoppers at the Breitscheidplatz market, killing 12 and injuring more than 70 others.
On Monday, visitors to the festive outdoor space saw new additions to the traditional bright lights, stollen cake and mulled wine: concrete barriers hidden behind Christmas trees and a heightened police presence.
"We are happy that the market is starting up again," said Martin Gelmer, the pastor for the Kaiser Wilhelm Memorial Church, which overlooks Breitscheidplatz.
"But at the same time we know what happened here: that people died here and that other people must now live with serious injuries," he told AFP, shortly after leading a service for the vendors.
Organiser AG City, which has also deployed teams of private security guards in orange vests, expects up to one million visitors by the time the market winds down on January 7.
It will close on the attack anniversary, when a memorial in the form of a gold-coloured crack in the ground with the names of the victims will be inaugurated.
Last year's horror weighed heavily on many present.
"You think about it... I don't feel so at ease," said Christa Okunick, 67, visiting from the western city of Dortmund.
Last year, she came to the Christmas market a week before the attack, an experience she couldn't put out of her mind on this visit.
"It is an unsafe place, and you can't protect it at all... I'm indeed a bit scared."
Others such as Noreen Moore, 73, visiting from the US state of Colorado, were unfazed.
"It's part of the German custom," she said, describing how she came to Berlin for the Christmas markets and hoped to visit as many as she could on her trip.
She felt "very comfortable" walking around, she said.
Interior Minister Thomas de Maiziere urged Germans not to be afraid to enjoy their time-honoured holiday markets, which attract 85 million visitors yearly across the country.
People should be "mindful but not fearful", he told Bild.
"Christmas markets are part of our life and culture."
The threat of another attack remains unchanged at a high level in Germany and Europe, said an interior ministry spokesman on Monday.
Other markets have tried different ways of incorporating bolstered security.
In the western city of Bochum, sandbags were wrapped as Christmas presents.
And the German city of Magdeburg invested 40,000 euros ($48,000) in concrete blocks made to look like Lego pieces, according to Bild.
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