A cage cup, also vas diatretum, plural diatreta, or "reticulated cup" is a type of luxury late Roman glass vessel, found from roughly the 4th century, and "the pinnacle of Roman achievements in glass-making". Diatreta consist of an inner beaker and an outer cage or shell of decoration that stands out from the body of the cup, to which it is attached by short stems or shanks. About fifty cups or, more often, fragments have survived, and there are only a few in near-complete condition. Most have a cage with circular geometrical patterns, often with an "inscription", or phrase in letters above the reticulated area as well. Some have a flange, or zone of projecting open-cut moulding, above the lower patterns and below the lettering (only illustrated here by the Cologne cup in the gallery). Even rarer are examples with scenes with figures, of which the Lycurgus Cup in the British Museum is the only complete example to survive, though there are other fragments. In this the rest of the "cage" is made up of a vine that entraps Lycurgus. None have a foot. All were clearly difficult to make, and no doubt very expensive, like the other spectacular type of luxury Roman glass, cameo glass objects like the Portland Vase. Both the technology used to make them and the way they were used are still the subject of some debate among specialists. Technology Cage cups, diatreta, are mentioned in Roman literature, and the dates assigned to examples (not necessarily by the same people) range from around the mid-third to the mid-4th century, at the same time as the late Roman cameo glass vessels. They appear to have been made of similar glasses, and there is also evidence that some late vessels may have been combinations of cameo and cage-cup techniques. The main division is between cups with figures, whether or not accompanied by reticulated patterns, and those without. Some have inscriptions and flanges with ovolo decoration; others do not. Most have a narrow beaker shape, but others a wider bowl-like one. Since the first publication on the subject in 1680 it has mostly been accepted that the cage cups were made by cutting and grinding a blank vessel of solid thick glass, a laborious technique at which the Greeks and Romans were very experienced from their passion for hardstone carvings and engraved gems in semi-precious stones. An alternative theory,