When two timbers join to become one unit, they are mated with a so-called “scarf joint”. Scarf joints come in many different styles, some more elaborate than others. This sill beam scarf joint is a rather simple one, as far as layout and cutting, goes and it is wisely located directly above a support pier.
This photo was taken before pegs were driven into each tenon, but if you look carefully you can see on the upper half of the scarf where the peg hole is marked.
Scarf joints were developed when taller trees became scarce and long spans had to be created with shorter pieces of timber. I think that timber framing is beautiful for its ingenuity and effective use of materials.