diff --git a/src/proto_alpha/bin_sc_rollup_node/dal_node_client.mli b/src/proto_alpha/bin_sc_rollup_node/dal_node_client.mli
index 15b832d4239a82834e0986c518ca69afccfbf0a6..b7a769149ed63a39aa8d18ceee91ec9b9bc29b81 100644
--- a/src/proto_alpha/bin_sc_rollup_node/dal_node_client.mli
+++ b/src/proto_alpha/bin_sc_rollup_node/dal_node_client.mli
@@ -44,7 +44,7 @@ class unix_cctxt :
 val make_unix_cctxt : Configuration.t -> cctxt
 
 val get_slot :
-  #cctxt -> ?trim_slot:bool -> Dal.Slot.header -> string tzresult Lwt.t
+  #cctxt -> ?trim_slot:bool -> Dal.Slot_header.t -> string tzresult Lwt.t
 
 val get_shard :
-  #cctxt -> Dal.Slot.header -> int -> Cryptobox.shard tzresult Lwt.t
+  #cctxt -> Dal.Slot_header.t -> int -> Cryptobox.shard tzresult Lwt.t
diff --git a/src/proto_alpha/lib_protocol/alpha_context.ml b/src/proto_alpha/lib_protocol/alpha_context.ml
index 0b4d291eb75aacfe96babdf8829f08a0ed801ef1..77b3de3910ae9d304926c16eeb11fa0c83c22d1d 100644
--- a/src/proto_alpha/lib_protocol/alpha_context.ml
+++ b/src/proto_alpha/lib_protocol/alpha_context.ml
@@ -109,6 +109,8 @@ module Dal = struct
     include Dal_slot_repr.Page
   end
 
+  module Slot_header = Dal_slot_repr.Header
+
   module Slot = struct
     include Dal_slot_repr
     include Dal_slot_storage
diff --git a/src/proto_alpha/lib_protocol/alpha_context.mli b/src/proto_alpha/lib_protocol/alpha_context.mli
index 6a073710a4ceeb798005d12e9e8ad5c224396959..0b6aefe149068988e66b712e63a77f4b49913f3c 100644
--- a/src/proto_alpha/lib_protocol/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/alpha_context.mli
@@ -2794,19 +2794,22 @@ module Dal : sig
     val equal : t -> t -> bool
   end
 
+  (** This module re-exports definitions from {!Dal_slot_repr.Header}. *)
+  module Slot_header : sig
+    type t = Dal.commitment
+
+    val zero : t
+  end
+
   (** This module re-exports definitions from {!Dal_slot_repr},
       {!Dal_slot_storage} and {!Raw_context.Dal}. *)
   module Slot : sig
-    type header = Dal.commitment
-
     type t = {
       published_level : Raw_level.t;
       index : Slot_index.t;
-      header : header;
+      header : Slot_header.t;
     }
 
-    val zero : header
-
     val encoding : t Data_encoding.t
 
     val pp : Format.formatter -> t -> unit
diff --git a/src/proto_alpha/lib_protocol/dal_slot_repr.ml b/src/proto_alpha/lib_protocol/dal_slot_repr.ml
index 58ece202ea6eb287c1f7917f7e9897a12922e179..af1bbc76fab9ea0a81d50d4af8871f63c88933c0 100644
--- a/src/proto_alpha/lib_protocol/dal_slot_repr.ml
+++ b/src/proto_alpha/lib_protocol/dal_slot_repr.ml
@@ -36,6 +36,8 @@ module Header = struct
 
   let pp ppf commitment =
     Format.fprintf ppf "%s" (Dal.Commitment.to_b58check commitment)
+
+  let zero = Dal.Commitment.zero
 end
 
 module Index = struct
@@ -61,11 +63,11 @@ module Index = struct
   let equal = Compare.Int.equal
 end
 
-type header = Header.t
-
-let zero = Dal.Commitment.zero
-
-type t = {published_level : Raw_level_repr.t; index : Index.t; header : header}
+type t = {
+  published_level : Raw_level_repr.t;
+  index : Index.t;
+  header : Header.t;
+}
 
 type slot = t
 
@@ -76,6 +78,15 @@ let slot_equal ({published_level; index; header} : t) s2 =
   && Index.equal index s2.index
   && Header.equal header s2.header
 
+let zero =
+  {
+    (* We don't expect to have any published slot at level
+       Raw_level_repr.root. *)
+    published_level = Raw_level_repr.root;
+    index = Index.zero;
+    header = Header.zero;
+  }
+
 module Slot_index = Index
 
 module Page = struct
@@ -241,7 +252,7 @@ module Slots_history = struct
 
     type history = (content, ptr) Skip_list.cell
 
-    type t = history option
+    type t = history
 
     let history_encoding =
       Skip_list.encoding Pointer_hash.encoding slot_encoding
@@ -249,11 +260,11 @@ module Slots_history = struct
     let equal_history : history -> history -> bool =
       Skip_list.equal Pointer_hash.equal slot_equal
 
-    let encoding = Data_encoding.option history_encoding
+    let encoding = history_encoding
 
-    let equal : t -> t -> bool = Option.equal equal_history
+    let equal : t -> t -> bool = equal_history
 
-    let genesis : t = None
+    let genesis : t = Skip_list.genesis (zero : slot)
 
     let hash_skip_list_cell cell =
       let current_slot = Skip_list.content cell in
@@ -290,17 +301,18 @@ module Slots_history = struct
 
     let add_confirmed_slot (t, cache) slot =
       let open Tzresult_syntax in
-      match t with
-      | None -> return (Some (Skip_list.genesis slot), cache)
-      | Some t ->
-          let content = slot in
-          let prev_cell_ptr = hash_skip_list_cell t in
-          let* cache = History_cache.remember prev_cell_ptr t cache in
-          return
-            ( Skip_list.next ~prev_cell:t ~prev_cell_ptr content |> Option.some,
-              cache )
-
-    let add_confirmed_slots t cache slots =
+      let* () =
+        error_when
+          Raw_level_repr.(slot.published_level <= zero.published_level)
+          (failwith
+             "No slot is supposed to be published at level \
+              'Raw_level_repr.root'")
+      in
+      let prev_cell_ptr = hash_skip_list_cell t in
+      let* cache = History_cache.remember prev_cell_ptr t cache in
+      return (Skip_list.next ~prev_cell:t ~prev_cell_ptr slot, cache)
+
+    let add_confirmed_slots (t : t) cache slots =
       List.fold_left_e add_confirmed_slot (t, cache) slots
 
     let add_confirmed_slots_no_cache =
diff --git a/src/proto_alpha/lib_protocol/dal_slot_repr.mli b/src/proto_alpha/lib_protocol/dal_slot_repr.mli
index 18ded1f945b557df98ea573d68cf1ea9faedf888..9f93381aab87c5c1ddce5c3700d6663f2af2daa7 100644
--- a/src/proto_alpha/lib_protocol/dal_slot_repr.mli
+++ b/src/proto_alpha/lib_protocol/dal_slot_repr.mli
@@ -50,6 +50,8 @@ module Header : sig
   type t = Dal.commitment
 
   val encoding : t Data_encoding.t
+
+  val zero : t
 end
 
 (** An `Index.t` is a possible value for a slot index. We assume this value
@@ -84,12 +86,14 @@ module Index : sig
   val equal : t -> t -> bool
 end
 
-type header = Header.t
-
 (** For Layer-1, a slot is described by the level at which it is published,
     the slot's index (in the list of slots), and the slot's header
     (KATE commitment hash). *)
-type t = {published_level : Raw_level_repr.t; index : Index.t; header : header}
+type t = {
+  published_level : Raw_level_repr.t;
+  index : Index.t;
+  header : Header.t;
+}
 
 type slot = t
 
@@ -132,8 +136,6 @@ end
 (** The encoding ensures the slot is always a non-negative number. *)
 val encoding : t Data_encoding.t
 
-val zero : header
-
 val pp : Format.formatter -> t -> unit
 
 (** Only one slot header is accepted per slot index. If two slots
diff --git a/src/proto_alpha/lib_protocol/test/helpers/operation_generator.ml b/src/proto_alpha/lib_protocol/test/helpers/operation_generator.ml
index 58b381a5be0a1d5d229a00c5390865298c79ea28..0709c58728e44a7876c840a66456516edd4f368e 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/operation_generator.ml
+++ b/src/proto_alpha/lib_protocol/test/helpers/operation_generator.ml
@@ -662,7 +662,7 @@ let generate_dal_publish_slot_header random_state :
   let gen_dal_publish _ =
     let published_level = Alpha_context.Raw_level.of_int32_exn Int32.zero in
     let index = Alpha_context.Dal.Slot_index.zero in
-    let header = Alpha_context.Dal.Slot.zero in
+    let header = Alpha_context.Dal.Slot_header.zero in
     let slot = Alpha_context.Dal.Slot.{published_level; index; header} in
     Dal_publish_slot_header {slot}
   in
diff --git a/src/proto_alpha/lib_protocol/test/integration/validate/manager_operation_helpers.ml b/src/proto_alpha/lib_protocol/test/integration/validate/manager_operation_helpers.ml
index c6e0d8fa4ad8f9e04b223b17f062131fe20719cd..b3394c31f09c1a3e6b87b40f08a2044642349ade 100644
--- a/src/proto_alpha/lib_protocol/test/integration/validate/manager_operation_helpers.ml
+++ b/src/proto_alpha/lib_protocol/test/integration/validate/manager_operation_helpers.ml
@@ -1028,7 +1028,7 @@ let mk_sc_rollup_return_bond (oinfos : operation_req) (infos : infos) =
 let mk_dal_publish_slot_header (oinfos : operation_req) (infos : infos) =
   let published_level = Alpha_context.Raw_level.of_int32_exn Int32.zero in
   let index = Alpha_context.Dal.Slot_index.zero in
-  let header = Alpha_context.Dal.Slot.zero in
+  let header = Alpha_context.Dal.Slot_header.zero in
   let slot = Alpha_context.Dal.Slot.{published_level; index; header} in
   Op.dal_publish_slot_header
     ?fee:oinfos.fee