What does the cryptic crossword clue "He attacked the Romans but turned tail at first (6)" mean?

The definition is "at first". The wordplay uses an anagram. anagram of TAIL (synonym="TAIL") + AT (synonym="AT") = ATTILA The answer is ATTILA.

He attacked the Romans but turned tail at first (6)

Guardian Cryptic #25215 | 19 Down | 2011-01-10 flower