During archaeological  excavations 242 Roman coins were found, and these were useful in dating the phases of construction.

Of equal interest were the post-Roman coins.

Five silver pennies of Edward I - III were found level with the surviving top of the arena wall. They lay in positions which they could not have reached by accidental percolation, and there can be little doubt that they were lost by those involved in 'robbing out' the stone for building use in the 14th century.

Also found were:
      7 Bristol tokens dated 1652
      1 Irish halfpenny of Charles II
      33 George I - III pennies and
      4 Victorian coins

- all evidence of trenches being cut into the structure for the recovery of building stone. 

When the stone 'robbers' found a wall they would dig a trench following its direction, remove the stone and backfill it. Archeologists look for evidence of these 'robber trenches' and can use them to draw up a plan of the site even when most of the stone has been removed. Fortunately a great deal of the original structure of Caerleon's amphitheatre remains.