Read: Emperor: the Gates of Rome by Conn Iggulden, 2003, 0385336608.
Recommended by a library patron. The book was okay, I enjoyed it. I like Steven Saylor's (no relation) novels better. Both are set in ancient Rome but I like Saylor's characters and use of setting.
Gaius and Marcus grow up together on the estate of Gaius's wealthy Senator father. Marcus is the family's ward, taken in since his mom is a high-class prostitute in Rome. Gaius's mother is mentally ill and his dad is often away in Rome. The estate is run by former gladiator Tubruk who is a sort-of father figure to both boys. As 12-year-olds they are trained by former soldier and gladiator Reinus. Renius is purposefully cruel.
Gaius's father is killed during Rome riots and a slave uprising. The two head to Rome with Reinus and Tubruk and are taken in by Gaius's maternal uncle, Marius. Maris is a Roman tribune and in conflict with the other tribune, Sulla.
Things happen. Death is easy. Slaves are treated well and treated horribly. The pecking order must be followed. Be careful with your political alignments. Sulla is maneuvered by Marius into a military campaign against a rebellious Greek king. Marius fortifies Rome in advance of Sulla's return. More violence. Marcus joins a Greek based Legion. Gaius soldiers with his uncle.
About half way through you're clued in that Gaius becomes Julius Caesar. Later on you learn Marcus is Brutus. I'll probably try the second one in the four part series.