Beginning in the 16th century and until steam-powered ships took over, British naval ships were rated according to the number of heavy cannon they carried. A ship of 100 or more guns was a First Rate line-of-battle ship. Second rates carried 90 to 98 guns; Third Rates, 64 to 89 guns; Fourth Rates, 50 to 60 guns. Frigates carrying 20 to 48 guns were fifth and sixth rated. The term "first rate" is now used to imply excellence.