The most common and most likely answer to this crossword clue is the 8 letter word TESTUDOS
T
E
S
T
U
D
O
S
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The straight part
We know that "troops once screened by these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case troops once screened by these = testudos.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 TESTUDOS mean?
TESTUDOS noun- A shelter formed by a body of troops by holding their shields or targets close together over their heads.
- A shelter of similar shape for miners, etc.
- A kind of lyre; so called in allusion to the lyre of Mercury, fabled to have been made of the shell of a tortoise.
- An encysted tumour.
- The fornix.