I would recommend Rubicon by Tom Holland, immensley readable and packed with information from everything from the Roman Slave Revolt to the two Ceasars and the end of the Roman Republic.
Sorry Gentlemen, have been very busy during the last weeks but would like to thank all of you for your recommendations! Nevertheless I have chosen none of the recommended books but stuck with one recommended in another thread - "The history of the Seven Years War in Germany" written by Johann Wilhelm von Archenholz. I was able to buy a copy printed in 1913, the oldest book I have so far and a very good read on this topic.