The opening of the Suez canal in 1869 made control of the area even more imperative for the European powers - France, Great Britain, Germany, Russia and even the United States, all sent missions of one kind or another to the area to establish a presence in the hope of acquiring influence.
Many of these included a religious initiative - like the Russians, who set up the Russian Compound in Jerusalem for pilgrims - as did, indeed the French and the Germans. Not a few were of academic intent intermingled with military undertones. Among the foremost of these was Great Britian. In 1865 Great Britain had set up "The Palestine Exploration fund" under the patronage of Queen Victoria herself and along with many military personnel came some of the greatest archæological scholars of the era among them the famous Charles Warren, himself an engineering officer.

During his stay and among his many researches, Robinson took the opportunity to examine from close range some protuberances on the southern end of the Western Wall - quite close to the south west corner. What he saw from up close (behind the tree) was this :-

Since the stones were clearly architectural "springers" (base or support-stones on which an arch of some kind could be erected), he proposed such an arch stretching across the Tyropeon Valley from the Temple mount, carrying pedestrian traffic up to the Jewish Quarter during the latter days of the Second Temple (30 B.C.E - 69 C.E.). This theory held credence until the re-unification of Jerusalem in 1967.
At that time and under renewed, unobstructed Jewish Sovereignty, modern archæologists got to work and dug down removing about 30 feet of rubble and dirt - two-thousand years of detritus. What they discovered was the end of the secondary main street running from the Damascus Gate, following the line of the Tyropeon valley until it finished running parallel alongside the Western Wall of Herod's Temple area and out through the southern wall of Jerusalem. The remains of shops along the street were discovered as well as the large building blocks from the top of the western wall, thrown down by Titus' army in their destruction of the Temple and still lying as they fell nearly 2000 years ago! It also became clear from the rubble, that Robinson's proposition was false and that - although an arch there had certainly been - it had not stretched across the valley up to the Jewish Quarter but had been a monumental staircase turning round and descending to the market street below. This famous sketch by Ritmeier, shows how the entire area must have looked on the eve of the destruction:-

A second arch - Wilson's Arch, can also be seen a little higher up the street. The stretch of wall between the two arches represents what is today, the Western (wailing) Wall.

I think this is a very nice representation of what the stairway must have looked like at the time of its construction - this is a fanciful representation of Herod inspecting his handiwork! (looking north along the western wall).