docs: add architecture overview (Mermaid) and link from README

README.md

@@ -26,7 +26,8 @@ privacy faithfully.
 Refer to the [Canton Whitepaper](https://www.canton.io/publications/canton-whitepaper.pdf) for further details.
 
 ## Availability
-
+For a high-level overview of Canton’s core components and how synchronization domains and participants interact, see  
+👉 [Architecture Overview](docs/architecture/overview.md)
 This repository hosts the open source version of Canton. The Enterprise version can be purchased from [Digital Asset](https://digitalasset.com/products).
 
 ## Running

docs/architecture/overview.md

@@ -0,0 +1,27 @@
+# Canton Architecture Overview
+
+This page gives a high-level view of key components and how they interact.
+
+```mermaid
+flowchart LR
+  subgraph Domain["Synchronization Domain"]
+    SQ[Sequencer]:::comp
+    MED[Mediator]:::comp
+  end
+
+  PN1[Participant Node A]:::node -->|Authenticated messages| SQ
+  PN2[Participant Node B]:::node -->|Authenticated messages| SQ
+
+  %% The mediator initiates the connection to the sequencer
+  MED -->|Initiates connection| SQ
+  %% Once established, messages flow bidirectionally
+  MED <--> SQ
+
+  classDef comp fill:#eee,stroke:#999,color:#000;
+  classDef node fill:#f7f7f7,stroke:#777,color:#000;
+```
+
+**Notes**
+- Participant nodes do **not** communicate directly; they interact through the sequencer.
+- The **mediator** initiates the connection to the **sequencer**; once established, the flow becomes bidirectional.
+- The **Topology Manager** is no longer part of Canton 3.x and is therefore omitted.