MS Excel 2010: Double click to copy down a row, but what about across columns

CTRL+D Uses the Fill Down command to copy the contents and format of the topmost cell of a selected range into the cells below.

This will go down a single column, but from, for example, A1 - A10, but what if I wanted to copy across mulitple columns, for example, A1 - F1???

Basically how do I Fill Across?