How to use only SQL to Concatenate Strings in Aggregation

USE CombinedArchaeologyDB

GO

SELECT S.SquareDesignation, --This is the element that we will group by
  STUFF(                                        --Stuff is a way of removing the first ', ' from the list
        (SELECT ', ' + CAST(L.LocusIdentity AS VARCHAR(MAX)) --This selects a ', ' concatenated with the locus identity 
         FROM ARCH_Locus AS L   --From the appropriate table
         WHERE L.SquareID=S.SquareID --This makes this a correlated subquery so that we only get the things we want
         FOR XML PATH(''),TYPE  --Specifies that we want XML with NO SURROUNDING ROW ELEMENT {PATH('')} and that we want it as XML type
        ).value('(./text())[1]','VARCHAR(MAX)'),1,2,'') AS Loci --The .value specifies a xquery of (./text())[1] resulting in type VARCHAR(MAX). The 1,2,'' Is part of STUFF that removes the first two characters. 
FROM ARCH_Square as S       --From the outer table
GROUP BY S.SquareID, S.SquareDesignation --Grouped by...