Ipotesi astronomiche sul foro della colonna augustea di Santa Maria in   Aracoeli
  The third column of the left row in the Basilica of Santa Maria in Aracoeli in Rome, has a hole carved in it, of probable astronomical use. The tube aims at a point a 116 degrees of azimut, East-South-East and 17.3 degrees of altitude, the Sun could be aimed in that direction at 07:00 UTC of 12 october and 7:25 UT of march 2, but the view is obstructed by the church's building. Same situation for the 3.9 magnitude alpha Monocerotis, visible 2000 years ago, taking into account the precession. Other hypotheses on the meridian astronomical use of this hole are here reviewed. In the case of solar observations it cannot be for meridian transits in Rome, since the lower transits occurs now at 24.5 degrees at winter solstice; we investigate the case of stellar transits, of declination 30.8 degrees South. Many alignments are possible leaving the azimut as free parameter, being the columun not in its original collocation, but here we investigate only the meridian transits, and no bright stars could have been seen through that hole, taking also into account the precession 2000 years ago. We conclude that this hole was probably not used for meridian observations. 
Costantino Sigismondi
physics.hist-ph