diff --git a/.gitmodules b/.gitmodules
index 1a5dab04f45..2119d642588 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -7,3 +7,6 @@
 [submodule "trees/public"]
 	path = trees/public
 	url = https://git.sr.ht/~jonsterling/public-trees
+[submodule "erct"]
+	path = erct
+	url = git@git.sr.ht:~jonsterling/elements-of-relative-category-theory
diff --git a/build.sh b/build.sh
index 594913d4c15..c17bcdb3ae5 100755
--- a/build.sh
+++ b/build.sh
@@ -1,4 +1,3 @@
 #!/bin/bash
 
-opam exec -- forester build --dev --base-url https://www.jonmsterling.com --root jms-0001 trees/
-# /Users/jon/Source/ocaml-forester/_build/default/bin/forester/main.exe build --dev --root=jms-0001 --base-url="https://www.jonmsterling.com" trees
+opam exec -- forester build --dev --base-url https://www.jonmsterling.com --root jms-0001 trees erct/trees
diff --git a/erct b/erct
new file mode 160000
index 00000000000..7a819489b67
--- /dev/null
+++ b/erct
@@ -0,0 +1 @@
+Subproject commit 7a819489b67d53bdf7a0bf9d4ad4f06a4e455f92