Nato has been holding a ceremony to welcome seven former communist eastern European countries as members of the 55-year-old alliance.
All of the new Nato members were part of the former communist bloc
The flags of Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia were raised for the first time at the Nato headquarters in Brussels.
It is the biggest ever expansion of Nato - set up in 1949 to defend western Europe against the Soviet Union.
The new countries joined Nato this week, taking the membership to 26.
The three Baltic republics, Estonia, Latvia and Lithuania, were once part of the Soviet Union, the very power against which Nato was created.
The expansion has caused concern in Russia, which says it may have to reconsider its defence strategies if its interests are ignored.
Russian Foreign Minister Sergei Lavrov was due to join the discussions at Nato headquarters later on Friday.
The BBC's Jonathan Marcus, in Brussels, says the fact that Russia is at the meeting at all, shows it realises that little can be done to halt Nato's eastward expansion.
Since the end of the Cold War, Nato's frontiers have moved steadily eastwards; first taking in Poland, Hungary and the Czech Republic, now extending to Romania and Bulgaria's Black Sea coast and - with the three Baltic republics - northwards almost to Finland.
Nato warplanes have been carrying out air patrols over the Baltic states since Monday, when the new members formally acceded. Four Belgian F-16 fighter planes are to be stationed in Lithuania.
At the ceremony on Friday morning, each of the new members' flags was raised in turn and their national anthems played. The new members then posed for an official photograph before heading into a ceremonial meeting of the North Atlantic Council.
The new members are joining an alliance that is currently undergoing rapid change.
Nato forces are engaged in peacekeeping in the Balkans; they are planning to expand their activities in Afghanistan; and there is also talk of a potential Nato role in Iraq.