Okay, let me rephrase that: A lot of the territory Rome ruled was conquered in Caesar's lifetime (Gaul, most of their core Asian possessions). Most of Rome's noteworthy cultural achievements happened after Caesar was dead. Caesar laid the groundwork for Augustus's form of government, which would survive in some form for nearly 1500 years. So starting an article about Rome's decline with Caesar is like writing an article about the decline of computer science and starting it with Turing.