A common size of land-holding was 12 × 12 = 144 plethra, = about 34 acres, a size corresponding to our medieval oxgang. In ancient Italy land was measured by the Roman decempeda or pertica, the 10-foot perch or rod, = 9·725 feet. A strip of land 120 × 4 Roman feet made an Actus, probably the breadth of a double furrow, up and down. The square actus, actus quadratus, = 30 acti = 120 × 120 feet, about 50 square rods. Two square acti made a Jugerum, the day’s work for a yoke of oxen, = 0·623 acre. Four square acti, bina jugera, made the Heredium, = 1·246 acre. How were the four square acti arranged? Were they in a square 240 × 240 feet? No doubt that would be the official form of the heredium; but it is probable that, as I have assumed for the Greek tetragyon of 4 square plethra, the 4 Roman acti would be, when convenient, practically arranged in a line, thus giving an agrarian unit of 480 × 120 feet and a furrow of about 160 yards, which is nearly one-tenth of the 5000 feet Roman mile.[15] Footnote 15: For evidence on the form of agrarian units see Notes in section 5 of this chapter. The official division of the field was based on the jugerum; this being divided, on the duodecimal or uncial system, into 12 unciæ, each of 24 square perticæ, the latter being the scruples, the qiráts, of the Roman land-ounce. Here we see the uncial system overshadowing the decempeda; for if the jugerum could be divided into 12 ounces of 240 × 10 feet and these into 24 scruples of 10 feet square, each of its two acti might also be divided into 100 sections of 12 feet square, or the double jugerum into 100 sections of 24 feet square. It is probable that this would be a more popular division than that based on the decempeda; for it is certain that a rod of 16 spans = 12 feet was used; it was the Græco-Roman _akena_ (from _akis_, goad), a gad or rod.