When the Nabataeans first settled in Petra and started building houses, they found that they needed to protect themselves from the flash floods in the area. They also needed a year-round supply of water for their own use. Therefore, to control floodwaters, the Nabateans built a dam at the entrance of the Siq and cut a tunnel in the rock to divert flood waters away from the Siq. The rock-cut tunnel is 88 meters long, and 12.8 meters high and redirects water through Wadi Mudhlim to reservoirs, water cisterns, and dams inside and outside Petra. As a consequence of the cessation of maintenance and cleaning operations, the dam at the Siq entrance has gradually deteriorated over time, resulting in floodwaters entering through the Siq instead of being diverted through the tunnel of Wadi Al-Mudhlim. The dam you see today was constructed in 1964 over the original Nabataean one, which was larger, to prevent a recurrence of a tragic flash flood that had earlier swept through the Siq. Towards the end of Wadi Mudhlim, there are niches that probably held baetyls, or god blocks, to protect the water, which was sacred to the Nabataeans.