diff --git a/PC-Mac/SOL.md b/PC-Mac/SOL.md
new file mode 100644
index 0000000..cc00532
--- /dev/null
+++ b/PC-Mac/SOL.md
@@ -0,0 +1,27 @@
+# Diablo 1 SOL File Format - Subtile Flags
+
+[1. Description](#1-description)  
+[2. File structure](#2-file-structure)  
+
+
+## 1. Description
+
+Diablo 1 SOL metadata file use the `.sol` file extension.  
+The SOL metadata file contains flags (one BYTE) for the subtiles.  
+
+
+## 2. File Structure
+
+```
+{SUBTILE FLAG} * {NUMBER OF SUBTILES}
+```
+
+The bits of the {SUBTILE FLAG} have the following meaning (starting from lowest bit):
+- `1` : blocks the walk-path
+- `2` : blocks the light
+- `3` : blocks missiles
+- `4` : enable transparency
+- `5` : left floor {CEL FRAME} has transparent part
+- `6` : right floor {CEL FRAME} has transparent part
+- `7` : ignore the two bits above (unused)
+- `8` : can be used as trap source and works as background for shrines and bookcases
diff --git a/README.md b/README.md
index 0e48fa4..57a340c 100644
--- a/README.md
+++ b/README.md
@@ -11,10 +11,11 @@ Most of the knowledge here comes from the Diablo 1 and Hellfire modding communit
 - [Diablo 1 CL2 File Format - Graphics](PC-Mac/CL2.md)
 - [Diablo 1 MIN and TIL File Formats - Level Graphics](PC-Mac/MIN-TIL.md)
 - [Diablo 1 DUN File Format - Level Maps](PC-Mac/DUN.md)
+- [Diablo 1 SOL File Format - Sub-Tile Flags](PC-Mac/SOL.md)
 
 
 ## PlayStation
 
 - [Diablo 1 DIR/BIN File Format - Archives](PSX/DIRBIN.md)
 
-*Work in progress: MPQ, SOL, AMP, PlayStation version formats.*
+*Work in progress: MPQ, AMP, PlayStation version formats.*