Translate doesn't work with vertex

Hey guys,

I'm completely new to processing, seems a magnificent tool!

But I have a problem which in the end comes to this prototype example:

size (600,600);
translate(width/2, height/2);
background(255);
stroke(0);
noFill();

//does work
beginShape();
vertex(0,0);
vertex(20,0);
vertex(20,20);
vertex(0,20);
vertex(0,0);
endShape();

//doesn't work, no square drawn
beginShape();
vertex(0,0);
translate(50,0);
vertex(0,0);
translate(0,50);
vertex(0,0);
translate(-50,0);
vertex(0,0);
translate(0,-50);
vertex(0,0);
endShape();

It would be nice for my further application if the second square would be drawn correctly as well (I know, this example is stupid, but it's the easiest way to explain my problem I think).

Does translate not work together with vertex or beginshape/endshape?

Thanks a lot for your help!

Martin