Possibly the only milestone surviving in Kilkenny (city). Maudlin Street used to be the road to Dublin, and the distance of 57 might refer to that.
<a href="//commons.wikimedia.org/wiki/User:A.-K._D." title="User:A.-K. D.">A.-K. D.</a>
<span class="int-own-work" lang="en">Own work</span>