Calculating Reconstruction Information
The process of building the Herodian Temple Mount real-time model required the reconciliation of excavation data with the functional requirements of the ancient city. In the case of Robinson's Arch, excavations established the location of the major pier that buttressed the weight of the monumental arch, the northwestern corner of the monumental staircase that connected the top of the platform with Tyropoeon Street below, and the secondary piers perpendicular to the street that carried the supporting vaults of the staircase. From this information, the reconstruction team had to make decisions about the form of the monumental staircase.
Based on the 21.25-meter height difference between the street level and the top of the platform, the reconstruction had to contain 106 steps (each with a rise of .2 m, or 7.87 inches). This is the equivalent of a seven-story office building. The first version of the structure grouped the stairs in three flights. Plotting the location of the secondary piers perpendicular to the street suggested that the north-south flight of stairs was broken by a series of landings. This change extended the length of the structure to 61.44 meters, pushing the southern-most edge into an area of the Jerusalem Archaeological Park not excavated down to the level of Herodian occupation. In the reconstruction, this area is shown as having a wide set of stairs rising from the street to the west with a generous landing before turning to the north. In the event of excavations to the Herodian level in that area, the model can be easily updated to reflect the new data. The last major change to Robinson's Arch was to reduce the width of the middle flight of stairs to match the excavation plan. This allowed the inclusion of a landing on the flight of stairs immediately above the arch.
As seen in its final form at the Ethan and Marla Davidson Center, the model of Robinson's Arch includes two miqva'ot (ritual baths) within the primary pier structure and handrails based on artifacts recovered in the IAA excavations.