The Roman stitch is a combination of the stockinette stitch and the seed stitch. For the basic Roman stitch, starting on an even number of stitches, you knit the first row and purl the second row (stockinette stitch). On the third row, you knit 1, purl 1 across the row, and on the fourth row, you purl 1, knit 1 across the row. The third and fourth rows are the seed stitch. You repeat these four rows for the pattern.
A variation of this pattern is to knit the first row, purl the second row, knit the third row, purl the fourth row, and on the fifth row, knit 1, purl 1 across, and on the sixth row, purl 1, knit 1 across. This creates a little wider stretch of stockinette pattern and looks particularly attractive on larger garments, such as sweaters.
Another variation of the Roman stitch creates a striped look when knitted. It is done on multiples of 2 plus 1 (for example, 14 plus 1 stitch = 15 stitches). On the first row, you knit 1, purl 1, knit 1; then purl 1, knit 1 across the rest of the row. You repeat this on the second row. Rows three and five are knitted. Rows four and six are purled.
There is also a Roman rib stitch (used for the bottom of sweaters and/or around the sleeves, the rims on caps, and around the wrists of gloves) that is patterned after the Roman stitch. To form this pattern, knit the first row and purl the second row. On rows three and four, knit 1, purl 1 across. Knit row five across and purl row six across. On rows seven and eight, purl 1, knit 1 across.
A lacy version of the Roman stitch is called the Roman stripe pattern. It is done on an even number of stitches. On the first row, you knit 1, yo (yarn over), knit 1; then, yo, knit 1 across to the last stitch and knit1. On the second row, knit 1; then purl across the row to the last stitch; knit 1. On the third row, you knit 1; then, k2tog (knit two stitches together) across the row to the last stitch and knit 1. On rows four and five, you knit 1; then yo, k2tog across the row to the last stitch; knit 1. Rows six and seven are knitted.