grrr, why can AI enter my cultural borders with ships?

[cordash]

I am not at war with any of them. I do not have open borders with any of them . I was under the impression that enemy units couldnt enter your cultural borders without inciting war or without having open borders? Does this rule not apply to ships? Sorry if this is a newb question, pls help

 

[Harry Haller]

There is one naval unit (the caravel?) that can enter your borders. It can only carry one non-combat unit (a spy, great person, etc).

 

[cordash]

ah ok that makes sense. Thank you

 

[Dragonlor]

Submarines can sneak around your territory as well.