The palace consisted mainly of two palace wings placed north and south of a large garden. Immediately north of the complex, in the area of today's Citadel and Jaffa Gate, Herod erected three huge towers, as an additional protection and last refuge in case of danger. These he called after people close to him - Hippicus after a friend, Phaesal after his brother, and Mariamne after his favourite wife. These towers strengthened the northwest corner of the First Wall, the city wall built by the Hasmoneans sometime around 142 BCE.
In 1878, Conrad Schick, a German architect and archaeologist, was allowed to explore and measure the tower of David. He found that in its lower courses, it was a solid structure of immense stones, Herodian in workmanship. From a comparison of its dimensions with those as given in Josephus, he concluded that it represented the remains of Herod's largest tower Phasael.
After World War I, the British removed the dilapidated Turkish barracks from the courtyard of the citadel, and discovered an old wall circling from the so-called tower of David toward the southwest. Evidently the present citadel had been built straddling the remains of this older wall. There were also traces of two salient towers. To determine the nature of this old wall and towers, and their relations to the rest of the structure, the Department of Antiquities began a series of careful soundings in 1934. Although the work was interrupted by the Arab-Jewish troubles and again by World War II, several preliminary reports have been published.
Mr. C. N. Johns, director of the excavations, believes that this old wall which has been traced across the courtyard of the citadel, is a segment of a city wall from the Jerusalem of the first century BCE. It may represent a portion of the wall re-built by Antipater, Herod's father, and strengthened about 24 BCE by Herod with the addition of three massive towers. Apparently it incorporated some earlier elements from previous fortifications on the site. How early these may be, remains to be determined.
No traces of the other two Herodian towers have been found thus far, nor of the palace. The Mariamme was probably to the east of Phasael. Johns believes that Hippicus was to the north of Phasael, and independent of the walls. The two salient towers recently discovered in the courtyard are definitely pre-Herodian.
In the 1970s, excavations outside the city wall disclosed the exit of a water drain belonging to Herod's Palace. It transported water from the palace into the Hinnom valley. In the kishle the other end was dug up. The pipe is big enough for humans to creep through. That also happened during the First Jewish War, when Jewish rebels fled the city via the sewers of Herod's palace. The pipe in the kishle could be one of those. The Kishle prison excavations were briefly open to the public in July 2011 and are, as of February 2016, accessible every Friday morning when guided tours are organised by the Tower of David Museum.
Until recently, no portion of Herod's palace proper—excluding, that is, the surrounding walls-and-towers complex—had ever been uncovered. In 2001, however, excavations disclosed two palace walls, constructed of the easily recognizable Herodian hewn giant blocks. Even these probably did not belong to the palace proper, but were part of the retaining walls for its base, a construction similar to that used by Herod at the Temple Mount. Excavations by Ruth Amiran and Avraham Eitan have also revealed some parts of the superstructure which included sections of painted plaster.
They excavated the north-western extremity of the city in the Hasmonean-Herodian period. One of the principal findings of their excavation in the Citadel was the complicated remains of stratum iv. This consists of a massive 3-4m high platform which supports the remains of two insulae of buildings which extend along both sides of a line. One room has been excavated on the eastern insula and nine rooms have been found off the western insula. However it is the massive platform which allowed the archaeologists to identify the site as Herod’s palace, according to Josephus’ lengthy description of it in book 5 of ‘The wars of the Jews’. They were able to assign the remains of stratus iv to subsidiary buildings of the Royal Palace.