The most impressive construction at Megiddo is underground. To ensure access to the spring at the bottom of the tel’s southwestern slope, engineers in the much-besieged city dug a 25-metre vertical shaft down to bedrock, then a 70-metre tunnel sloping up to the spring. The tunnel was cut from both ends and the two gangs of workers had to make only a small correction before they met. Then the outside entrance to the spring was sealed with a massive stone wall and concealed with earth so a besieging enemy could not discover it. This monumental project was apparently undertaken during the reign of King Ahab, about 150 years before King Hezekiah quarried his water tunnel in Jerusalem. When it was completed, residents standing at the top of the shaft could lower buckets to draw water without entering the tunnel or leaving the city. Modern stairways — 187 steps down and 77 steps up — allow hardy visitors to view this engineering feat from the inside.