Roman Mosaic

Daniel Ruiz Agulera retweeted this [url=https://twitter.com/Britanniacomms/status/852417646855413761]sweet Roman era mosiac[/url] in England. So, morning GeoGebra project. The original mosaic had 40 isosceles triangles around and 19 rows. What kept the artist from that 20th row?

Information: Roman Mosaic