Internal borders may be crossed at any point without a border check on persons,
irrespective of their nationality, being carried out.
However, the abolition of border control at internal borders shall not affect, inter alia,
the exercise of police powers by the competent national authorities, security checks
on persons carried out at ports, or the possibility for a Member State to oblige a
person to hold or carry papers and documents.
For the purpose of the Schengen Border Control, “internal borders” means “(a) the
common land borders, including river and lake borders, of the Member States, (b)
the airports of the Member States for internal flights, and (c) sea, river and lake ports
of the Member States for regular ferry connections.”