Gates are common dual lands that can tap for either of two different colors of mana (one for each guild). That it is a Gate doesn't mean anything on its own, but it's a marker that other cards look for. The subtype only appears on cards named "Guildgate", there are ten Guildgates, one for every Guild of Ravnica. Five of them were printed in each of the first two sets of the block. In the third set they were all reprinted. 
According to Mark Rosewater the Gates weren't supposed to pull focus early, so there were just enough cards mentioning Gates to keep players from asking why the Gate subtype even existed.  In the third set of the block their full potential was used.
- Maze's End
- Opal Lake Gatekeepers
- Saruli Gatekeepers
- Smelt-Ward Gatekeepers
- Sunspire Gatekeepers
- Ubul Sar Gatekeepers
Return to Ravnica
"The guilds of Ravnica"
"Will destroy each other"
Order of the Guilds as depicted in Tablet of the Guilds
- UADLR (Azorius)
- NZADN (Orzhov)
- LENP (Dimir)
- EIDA (Izzet)
- SSTC (Rakdos)
- SSHT (Golgari)
- TOER (Gruul)
- HLGE (Boros)
- EVUB (Selesnya)
- MEIO (Simic)
"Unless the maze is solved and the guildpact reborn"
- Trick Jarrett. (April 17, 2013.) "Zoomed Guildgates", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Mark Rosewater. (October 08, 2012.) "City Mail", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Trick Jarrett. (May 24, 2013.) "Embedding Puzzle", Daily MTG, magicthegathering.com, Wizards of the Coast.
|Basic lands||Plains • Island • Swamp • Mountain • Forest|
|Concepts||Barry's Land • Cave/City|
|No (colors of) mana||Fetch lands • Guildhomes • Loci • Urzatron|
|One color of mana||Artifact lands • Depletion lands • Sac lands • Storage lands|
|Two colors of mana|| Check lands • Depletion duals • Dual lands • Filter lands |
Gates • Karoo lands • Pain lands • Sac lands • Shock lands
Slow lands • Storage duals • Tainted lands • Taplands
|Three colors of mana||Triple lands|