Opus spicatum, literally "spiked work," is a type of masonry construction used in Roman and medieval times. It consists of bricks, tiles or cut stone laid in a herringbone pattern.
Please see the photos of the Opus Spicatum floors of the Villa di Tiberio in Sperlonga, where the wonderful sculptural group of Polyphemus with Ulysses was found.
Also at the Mercati Traianei there is an example of particularly beautiful Opus Spicatum.