Line B was not in operation until 1985, which you may find slightly surprising, considering it appears to be the oldest of the lines. A different construction technique was used on much of this line to that which had been used previously, whereby the tunnel was bored below the ground, as opposed to being pre-constructed and then dropped into the ground and covered. Most of the stations on lines A and C had been constructed using the cut and cover technique, with the exception of Náměstí Míru, which was actually the first station to be deep bored and is still the deepest at 52m.