On the left side or north side of this Hole and slightly overlapping this hole was the site of what is believed to be the removed monument of the bronze equestrian statue of Domitian (Equus Domitiani). At that location there is a rectangle of blocks (7.8 m x 12.2 m) in the Forum pavement. And below that a concrete base but unlike the Hole's concrete base this base doesn't block the Gladiator's tunnels.
This formed the foundation for the large pedestal that supported the huge Domitian equestrian statue. Also Domitian wanted to show that he had a bigger one than Julius Caesar :-) . Caesar had a large equestrian statue in the nearby Forum of Caesar. Statius mentions the "massive base" which I assume to mean it was very high.
The statue faced east with his horse striding forward (one leg in the air), Domitian in military uniform with General's cloak and sword, on his left hand was a figure of Minerva holding a shield and his right hand was extended in a gesture of peace. This bronze statue was put there in 91 AD in honor of Domitian's campaign in Germany.
In 96 AD Domitian is assassinated and the Senate decreed a 'damnatio memoriae' on him. The statue is destroyed and the pedestal is very likely removed. There is an ancient urban legend that his widow collected pieces of a smashed statue of her husband and had them pieced back together. She then had the statue erected on the Clivus Capitolinus in full view of the Senate House (Curia). Very very unlikely with a damnatio memoriae against him plus his loving wife was in on his assassination. And even if true it would not have been this huge equestrian statue as it is sometimes suggested.
But that is not to say that this urban legend isn't based on some facts. Procopius about 550 AD writing in his Anecdota (Secret History) says that there was a pieced together bronze statue in that location during his lifetime which he says was Domitian; or was this just part of the urban legend? So the statue seems to be a fact and this is the urban legend to explain it in his lifetime?
"...the Senate passed a decree that not even the name of this emperor should remain in inscriptions, nor any statue or portrait of him be preserved.Next: #17.8: Equestrian Statue of Constantine?
Certainly from the inscriptions everywhere in Rome, and wherever else his name had been inscribed, it was chiseled out, as can still be seen, leaving all the rest intact; and nowhere in the Roman Empire is there a single likeness of him except for a solitary bronze statue, which survived in the following way.
Domitian's consort was a woman of good birth, and highly respected, who had herself never done the least wrong to any man alive, or approved a single one of her husband's actions. So she was very highly esteemed, and the Senate at this time sent for her and invited her to ask for anything she liked. She made only one request -- that she might take Domitian's body and bury it, and set up a bronze statue of him in a place of her own choosing. The Senate agreed to this, and the widow, wishing to leave to later generations a monument to the inhumanity of those who had carved up her husband, devised the following plan.
Having collected Domitian's flesh, she put the pieces together carefully and fitted them to each other. Then she stitched the whole body together and showed it to the sculptors, asking them to make a bronze statue portraying the tragic end of the dead man.
The artists produced the statue without loss of time, and the widow took it and erected it in the street that leads up to the Capitol, on the right-hand side as you go there from the Forum: it showed the appearance and the tragic end of Domitian, and does so to this day."