An Echo is an alternate reality that is nearly identical to a point in Homeline's past.
All books set in historical periods can be treated as Echo realties. Many cover huge periods of history:
- GURPS Arabian Nights: events 8000 BCE to 1307 with emphasis on the Golden Age of Islam
- GURPS Aztecs: events in Mesoamerica 8000 BCE to 1525
- Echo-Greece: Greece 1100 to 323 BCE
- The Last Spartan from GURPS All-Star Jam 2004.
- Echo-Rome: Rome and its empire 753 BCE to 476 CE
- GURPS Middle Ages 1: Medieval (650 to 1485) England
- GURPS Crusades: (1054 to 1291)
- GURPS Japan: Japan 1457 to 1868
- GURPS Swashbucklers: (1559 to 1815)
- GURPS Old West: United States 1800 to 1900
- GURPS Cops: (1667 to 2001)
- Renaissance: several GURPS books (14th to 17th century)
- "Airships" in GURPS All-Star Jam 2004: (1852 to 1937)
"Infinity names echoes based on the number of years the echo’s local present lags behind Homeline"
For example "An echo with a local present date of 1776 would be Echo 251, or 251 Minus (both names get used interchangeably), since 1776 is 251 years behind Homeline’s present date of 2027."
So something like "Echo -222" would NOT be an Echo of 222 BCE but rather an Echo of whatever is 222 years behind Homeline’s present date which likely is c 2038 making it an Echo of c 1816.