The fylfot or fylfot cross (ˈfɪlfɒt ) and its mirror image, the gammadion are a type of swastika associated with medieval Anglo-Saxon culture. It is a cross with perpendicular extensions, usually at 90° or close angles, radiating in the same direction. However - at least in modern heraldry texts, such as Friar and Woodcock & Robinson (see ) - the fylfot differs somewhat from the archetypal form of the swastika: always upright and typically with truncated limbs, as shown in the figure at right. The most commonly cited etymology for this is that it comes from the notion common among 19th-century antiquarians, but based on only a single 1500 manuscript, that it was used to fill empty space at the foot of stained-glass windows in medieval churches. This etymology is often cited in modern dictionaries (such as the Collins English Dictionary and Merriam-Webster Online). The fylfot, together with its sister figures, the gammadion and the swastika, has been found in a great variety of contexts over the centuries. It has occurred in both secular and religious contexts in the British Isles, elsewhere in Europe, in Asia Minor and in Africa. The gammadion is associated more with Byzantium, Rome and Graeco-Roman culture on the one hand, whereas the fylfot is associated more with Celtic and Anglo-Saxon culture on the other. Although the gammadion is very similar to the fylfot in appearance, it is thought to have originated from the conjunction of four capital 'Gammas' (, the third letter of the Greek alphabet) but that the similarity of the symbols is coincidental. Both of these swastika-like crosses may have been indigenous to the British Isles before the Roman invasion. Certainly they were in evidence a thousand years earlier but these may have been largely imports. They were certainly substantially in evidence during the Romano-British period with widespread examples of the duplicated Greek fret motif appearing on mosaics. After the withdrawal of the Romans in the early 5th century there followed the Anglo-Saxon and Jutish migrations.