Polish Prime Minister Beata Szydło in Rome Saturday | Andreas Solaro/AFP via Getty Images EU to move in different speeds despite Polish reservations Text of the Rome Declaration says countries will move in the same direction but ‘at different paces and intensity.’

ROME — The EU will move on with further integration without always waiting for the stragglers, European leaders pledged in Rome Saturday.

"We will act together, at different paces and intensity where necessary, while moving in the same direction," the declaration signed by EU leaders on the bloc's 60th anniversary said.

It added that this would happen "as we have done in the past, in line with the Treaties and keeping the door open to those who want to join later," a move to accommodate criticism most articulately voiced by Polish Prime Minister Beata Szydło.

German Chancellor Angela Merkel echoed the softeners in the text when she told reporters that "we want to get in the same direction" but spoke of a multispeed EU as a reality: "A Europe of different speeds doesn't mean that it's not a common Europe," she said after the ceremony.

Luxemburgish Prime Minister Xavier Bettel told the AP that he "preferred a two-speed Europe to a cul-de-sac and no speed at all." The two-speed idea, he claimed, was originally one by the Benelux countries. "We in Benelux were alone at the beginning, but then one country after other joined because we saw that certain countries took us as hostages," he said, referring to Poland's unsuccessful fight against European Council President Donald Tusk's reappointment earlier this month.

Tusk called for those who are unhappy to work constructively together. "Today it is not enough to call for unity and to protest against multiple speeds," he said in a speech in front of the 27 EU leaders (minus Britain's Theresa May who is busy writing a letter to formally trigger Article 50 that will be delivered in Brussels on Wednesday).

"It is much more important that we all respect our common rules such as human rights and civil liberties, freedom of speech and freedom of assembly, checks and balances, and the rule of law," Tusk said, referring to his home Poland and echoing repeated calls by the European Commission for the Warsaw government to respect judicial independence.

"Europe as a political entity will either be united, or will not be at all," Tusk said, adding that "the unity of Europe is not a bureaucratic model. It is a set of common values and democratic standards."

The summit marked the signature of the Treaties of Rome in 1957, which Commission president Jean-Claude Juncker praised as having "sealed our Union forevermore." He said the people in the room should be proud of having seen decades of peace on the EU's territory.

"After so many wars, so many battles — why are we not proud of this? Because it wasn't our generation but our predecessors?" Juncker said.

Tusk drew more concrete lessons from history. "Today in Rome we are renewing the unique alliance of free nations," Tusk said. The "great predecessors" of today's leaders "at that time did not discuss multiple speeds, they did not devise exits, but despite all the tragic circumstances of the recent history, they placed all their faith in the unity of Europe," Tusk said.