The Roman invasion primary introduced an improved architecture and infrastructure. This included roads (and specifically straight long-distance roads), and many modern roads still follow the plan decided upon by the Romans. Other elements of the landcape that the Romans introduced are the aqueducts, forts and central heating. Romans also founded cities, and many modern cities with "c(h)ester" in the name go back to the Roman times.
Furthermore, Romans spoke Latin, and many words in today's English have a Latin origin.
Romans also had a legal system, and the modern Legal system still benefits from its legacy.