As a detective trying to uncover the mystery of the crossword clue ‘Start of a boast by Julius Caesar’, the first thought that comes to mind is Julius Caesar’s famous phrase ‘Veni, Vidi, Vici’, which means ‘I came, I saw, I conquered’. This phrase is widely known, but only the ‘start’ of the phrase is required to solve the crossword clue. It’s safe to assume that the missing word must be the first part of the phrase before ‘I came’, which leads to the answer ‘VENI’. Additionally, knowing that Julius Caesar was a successful military commander, it’s highly plausible that his boast would be centered around his military conquests, lending further support to the answer ‘VENI’ as the start of his famous proclamation. With this logical deduction, the mystery of the crossword clue has been solved, and the answer is ‘VENI’ – a simple yet powerful expression that perfectly captures the military might of the great Julius Caesar.