The pointed arc appeared even in romanesque architecture, but it's a main feature in gotic style. In a [i]normal gotic pointed arc[/i] the midpoints of the two circular arcs are replaced from the centre of the window unto the corners of it. In the pointed arc you can draw a equilateral triangle.[br][b]Drag the green point in the applet to the left[/b].

By verticalizing the vault, one could economise on the width of the wall.