Janus was the Roman God of boundaries. Many homes had a shrine to Janus at the entrance. The two faced god looked inwards and outwards at the same time. He was the God of doormen.
In the Roman Forum stood the Temple of Janus, an arched portico which could be closed by two gates. The gates were shut in time of peace and opened in time of War. For most of the history of Rome the gates remained open.
Janus also marks the boundary of the year, giving us the name for the Month of January.
Amoretti IV: by Edmund Spenser
New year forth looking out of Janus gate,
doth seem to promise hope of new delight:
And bidding the old Adieu, his passed date
bids all old thoughts to die in dumpish spright
and calling forth out of sad Winters night,
fresh love, that long hath slept in cheerless bower:
Wills him awake, and soon about him dight
his wanton wings and darts of deadly power.
For lusty spring now in his timely hour,
is ready to come forth him to receive:
And warns the Earth with diverse coloured flower,
to deck herself, and her fair mantle weave.
Then you fair flower, in whom fresh youth doth reign,
prepare yourself new love to entertain.