An example of a rare solidus of Constantine I "The Great", 307-337.  This type is known as the "Eyes to God", with Constantine glancing towards the Heavens.  Struck in Sirmium in 324-5 this piece is at the beginning of the new coinage type, the Solidus.  This piece weighs 4.42g and is one (if not the) nicest pieces of its type available.