How is the American system of government similar to-and different from-the Roman Republic?

The legislative branches are different because in the United States we have a house of representatives and a senate (congress). In a roman republic there is a sentence and a assembly. The legal codes are different. In a roman republic all laws are written in the 12 tables. In the USA we write our laws in a constitution. Our judicial branches are different because in the USA we have 9 justices that serve for life, unlike a roman republic where there is 8 judges that serve for a term of 1 year