The most common and most likely answer to this crossword clue is the 12 letter word CORNERSTONES
I've seen this crossword clue in The Times
C
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More clues leading to the result CORNERSTONES
Buddy explains!

The straight part
We know that "bases" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bases = cornerstones.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CORNERSTONES mean?
CORNERSTONES noun- A stone forming the base at the corner of a building.
- Such a stone used ceremonially, often inscribed with the architect's and owner's names, dates and other details.
- That which is prominent, fundamental, noteworthy, or central.