Try to walk past.

None of the other travellers halt to show the guards any sort of authentification, so assume access to the city is open to everyone. You walk on, not too hasty, not too slow, for you don't want to appear suspicious. As you reach the area underneath the massive bulwark, a tunnel of several meters length, you are overcome by the feeling of having been spotted.

And, really, as you try to make your through the crowd, you notice from the corner of your eye, one guard hes left her posts and is coming towards you quickly. In front of you, a slow-moving ox wagon is blocking the way. There is no chance of getting away undetected. Maybe a hasty flight could be succesful. But should you risk that?