Early Christian traveled from the middle east to all directions to Rome with Saint Paul but also India and Africa.  Personal Relationship with god as well of the promise of good afterlife swayed rome in to making it is primary religion.

Early example of Christian art, c.420, showing Christ crucified and Judas hanging.
http://mattstone.blogs.com/photos/celtic_icons/early-christian-art.html

5th Century Mosaics in the Apse of the Basilica di Santa Pudenziana
http://photographiedujour.wordpress.com/2010/04/20/5th-century-mosaics/

Samson and the Lion. Wall-painting, c. 350-400. Via Latina Catacomb, Rome.  Could it be related to Daniel and the Lions?

http://www.ou.edu/class/ahi4263/byzhtml/p01-04.html

5th Century Mosaics in the Apse of Santa Maria Maggiore

http://photographiedujour.wordpress.com/2010/04/20/5th-century-mosaics/

The Good Shepherd, praying figures. Wall-painting. Catacomb of Priscilla, Rome.

http://www.ou.edu/class/ahi4263/byzhtml/p01-04.html

The Good shepherd 

http://www.elcamino.edu/faculty/eatherton/earlycristian.html

Christianity was brought to many places in the world.

http://mattstone.blogs.com/christian/2011/02/indian-jesus-art.html

A minature of the virgin Mary and baby Jesus in Persian style

http://mattstone.blogs.com/photos/christian_art_middle_east/virgin_mary_and_jesus_old_persian_miniature.html

Christianity about personal God.

http://en.wikipedia.org/wiki/File:Michelangelo_-_Creation_of_Adam.jpg

cross takes many shapes and sizes.

http://commons.wikimedia.org/wiki/File:Monogram_of_Christ_(Chrismon),_500s_AD,_Early_Byzantine,_perhaps_Syria,_gold_sheet,_gold_wire,_and_garnets_-_Cleveland_Museum_of_Art_-_DSC08363.JPG